Viticulture

Grapes are a unique agricultural product. While more than half go toward the production of wine, they are also grown to be dried into raisins or eaten fresh. Grapes command more return per acre than almost any other plant, and in 2018, a single hectare of grand cru vineyard in Burgundy cost over seven million dollars on average. Further, unlike many crops that are planted each growing season, vineyards are a long-term investment—they require several years to become established and are designed to survive for decades.

Unlike many commodity plants, the profitability of wine grapes is driven by quality, which includes the grape’s ability to convey a unique sense of place. While other agricultural crops look to new varieties for flavor improvement, disease resistance, and adaptations to climate, most wine producers rely on a small number of established cultivars. Site selection and vineyard practices, however, are critical, since improvement is achieved through management of the vine’s environment.

Domestication of the Grapevine

Grapes were one of the first fruits to be domesticated by humans. In ancient times, they were prized for their high levels of sugar, a source of both nutrition and novelty. Most of the grape varieties used in wine production belong to a single species, Vitis vinifera, which was first domesticated from wild grapevines, called Vitis vinifera subsp. sylvestris (or Vitis sylvestris), at least 7,000 years ago in the land between the Black, Caspian, and Mediterranean Seas. As nomadic people settled into an agrarian lifestyle, they carried grapevines south to Mesopotamia. Domestic vinifera grapes were spread from the Fertile Crescent throughout the Mediterranean and Europe, driven by the westward migration of farming communities and, eventually, the expansion of the Roman Empire. Vitis sylvestris is native to Europe and Western Asia, and wild grapevines still inhabit these areas. Some evidence indicates that there may have been other centers of domestication of Vitis sylvestris, including sites in the Iberian Peninsula and Southern Italy. 

Over time, a collection of grape varieties was generated through the process of evolution, breeding, and human selection. Today, roughly 10,000 grape cultivars exist, with over 1,400 in commercial production, and grapegrowing has spread to hospitable zones throughout the world.

Grapevines are lianas: unlike trees, they do not produce extensive wooden support systems but are instead “structural parasites,” climbing on trees for support. They are also phototrophs, or sunseekers, and invest most of their energy into producing leaves and tall shoots, since rapid vertical growth is essential for competition with other plants for vital sunlight. In nature, grapevines invest little energy in fruit production, yielding just enough scraggly clusters to ensure proliferation. Wild vines are also dioecious, which means that both male and females plants exist, and successful fertilization relies on wind and insects for pollination. Male plants bare no fruit, and female plants are only fruitful when a male plant is nearby.

By contrast, since domesticated grapevines are cultivated for their fruit, they have been selected and managed to be prolific. Hermaphroditic, self-pollinating varieties were likely chosen initially, since these vines would have reliably produced more fruit. In addition to high yields, the selection of vines suitable for agriculture favored those with other beneficial characteristics, including large clusters, adaptations to the growing environment, and resistance to disease. The ability to attain the high sugar concentrations necessary for wine production, as well as taste, aroma, and appearance, also factored into selection. Analogous to a house cat and a lion, domestic vines have diverged significantly from those found in nature.

While the romantic notion of a vineyard paints it as a natural space with little intervention, it is more akin to a highly cultivated garden, organized for both ease of use and optimization of yields and fruit quality. Rows facilitate management and allow tractors and other equipment to access the vines easily. Grapes are propagated vegetatively, generally grafted to a different species’ roots, and trained into small shrubs to facilitate management. Annual pruning dictates the number of shoots that will form in the following year and where they will be located. Growers often impose moderately stressful conditions, such as limited water availability, to encourage the vine to limit its vegetative growth and concentrate its energy on fruit production. By taming and training them, humans have coaxed vines to defy their nature in order to be cultivated effectively for food and wine production.

Vine Anatomy

Grapevines are perennial, deciduous plants that have a permanent woody frame consisting of a trunk, cordons, canes, and spur positions. Below the ground, an extensive root system anchors the vine and provides an interface with the soil, which supplies water and nutrients to the plant. A vine’s root system is mostly located within the top three feet of soil and consists of mature roots, which survive year to year, and smaller feeder roots, which grow anew each year. Often, Vitis vinifera is grafted onto a phylloxera-resistant rootstock. Grafted vines consist of an above-the-ground portion called the scion, which is joined to the rootstock at the graft union, visible a few inches above the vineyard floor. Some rootstock species develop deep root systems, while others grow more laterally.

A grapevine’s trunk is analogous to that of a tree; it’s the permanent, vertical structure. Cordons, canes, or spur positions may be attached to the trunk, though the vine’s form will ultimately depend on pruning decisions made during the first few years of the vine’s life. 

Canes are shoots grown in the previous growing season that have lignified, or turned brown. After pruning, they are generally one to four feet long. Spurs, however, are canes that have been trimmed to a length of several inches. Cordons are horizontal extensions of the trunk and have a number of spur positions located along them. Along a cane, there are dormant buds, and spurs generally contain between one and three buds. During the growing season, these buds develop into fruiting shoots. Every few inches along each shoot, there are nodes, which resemble knuckles, and the portion of stem between nodes is called the internode. Leaves, buds, clusters, and tendrils are joined to each shoot at the node. Collectively, all of the vegetative green growth that develops during the growing season is called the canopy.

Two types of buds are located at each node, between the leaf and the stem: lateral buds and dormant buds. Each bud contains a highly compressed potential shoot. Lateral buds develop into shoots called laterals during the current growing season. These are side shoots that branch off of the main fruiting shoots. They are typically non-fruiting but may produce small clusters known as second crop. Laterals are often trimmed or removed through canopy management to prevent overcrowding and shading. Dormant buds, also called latent buds, spend the year maturing and develop into shoots in future years. As a rule, the dormant buds that formed last year, on canes and spurs from one-year-old wood, are the most fruitful. Dormant buds on older wood may also develop into unwanted shoots called suckers. Generally, suckers will not produce any fruit, and they are removed while they are small.

Two types of buds are located at each node, between the leaf and the stem: lateral buds and dormant buds. Each bud contains a highly compressed potential shoot. Lateral buds develop into shoots called laterals during the current growing season. These are side shoots that branch off of the main fruiting shoots. They are typically non-fruiting but may produce small clusters known as second crop. Laterals are often trimmed or removed through canopy management to prevent overcrowding and shading. Dormant buds, also called latent buds, spend the year maturing and develop into shoots in future years. As a rule, the dormant buds that formed last year, on canes and spurs from one-year-old wood, are the most fruitful. Dormant buds on older wood may also develop into unwanted shoots called suckers. Generally, suckers will not produce any fruit, and they are removed while they are small.

At each node, a single leaf develops, adjacent to the buds. Leaves are the powerhouse of grapevines, where photosynthesis takes place, and petioles are their stems, connecting leaf and shoot. 

Clusters are located at nodes near the base of the vine. Most shoots contain between one and three clusters, with two being most common, though the typical number varies by grape variety. Carignan, for example, is known for producing three clusters per shoot. The area of the vine where the fruit is growing is described as the fruit zone. Long, thin coils called tendrils support the vine by wrapping around and attaching to trellises, trees, or other supports. Technically, they are modified flower clusters, though the two bear no resemblance to each other. Clusters and tendrils develop along each shoot in a “hit, hit, miss” pattern. The first few nodes closest to the base of the vine typically have neither. Then, every two nodes have either a cluster or a tendril, while every third node has neither, with the pattern continuing up the shoot.

Ampelography is the science of identifying grape varieties based on morphology. Clusters and berries vary in shape and size, and, along with leaf characteristics and the vine’s overall growth patterns, these attributes are used to identify grape species and varieties based on their unique patterns.

Vine Balance

A vine with ample water and nutrients will develop a large canopy with fast-growing shoots. Vine vigor refers to the amount of vegetative growth produced by a vine, and it is assessed through several markers, including shoot length and diameter, the number of shoots per vine, and the vine’s tendency to produce laterals and suckers. Vigor may be quantified through pruning weight, which is literally the weight of the material that is removed from the vine at pruning, sampled across a selection of vines.

A vine’s capacity is the optimum amount of fruit, or yield, it is able to produce, given its specific conditions. Vines that carry too much fruit for their frame may not be able to successfully ripen it, especially in marginal climates, and will weaken over time, further reducing capacity. On the other hand, if too little fruit is left, the vine will become more vigorous, and the amount of fruit produced will gradually decrease. There is a general belief that balanced vines make balanced wines. Vine balance considers vegetative versus fruit growth. The Ravaz Index, the ratio of fruit weight to pruning weight, is one metric used for assessment. Ratios of 4 to 10 are generally considered balanced. Growers also look at the length of shoots and internodes, targeting three- to four-inch internodes and roughly four-foot shoots.

Growers coax vines toward balance through planting decisions, including choice of rootstock and trellis systems, as well as vineyard operations, such as pruning and irrigation. Balanced vines pay off, maximizing yields and fruit quality. Yet it’s important to recognize that balance can take many forms. Larger vines have more capacity for fruit production, and vines grown on fertile soils will have more vigor and thus more capacity than those grown on weaker soils. In this scenario, the vine may be more balanced carrying five tons per acre rather than half of that. Appropriate yields should not be prescribed without understanding the conditions of the site.

Grapevine Taxonomy

Vitis vinifera, also called the European grapevine, includes many of the wine and table grapes. It belongs to the family Vitacae, along with other common vine plants like Boston ivy and Virginia creeper. Most cultivated grape species belong to the genus Vitis and have 38 chromosomes, while others belong to the genus Muscadinia, formerly considered a subspecies of Vitis, with 40 chromosomes. Beyond vinifera, several other Vitis species are significant in viticulture. Vitis rupestris, Vitis riparia, and Vitis berlandieri are common rootstock species, and Vitis labrusca, Muscadinia rotundifolia, and Vitis amurensis are occasionally used in winemaking. Within each species, there are many cultivars, often called varieties in a wine context.

Both species and varieties have been interbred. The offspring of two varieties belonging to the same species are known as crossings, and examples include Chardonnay, Riesling, Merlot, and almost all other cultivars used in winemaking. The products of interspecies breeding are called hybrids; rootstocks and niche wine grapes like Rondo, Chambourcin, and Vidal Blanc are examples. Crossings and hybrids have been bred to incorporate the desirable characteristics of both parents. For instance, Norton is a hybrid that combines the cold hardiness and resistance to fungal diseases of Vitis labrusca, with a flavor profile more similar to vinifera. (Labrusca varieties are often marked by a grapey flavor described as “foxy” that is generally not preferred in wine.) Throughout history, grape breeding has occasionally been intentional but more often occurs in nature. 

Cultivars 

Crossings of Vitis vinifera are responsible for the tens of thousands of cultivars that exist. Pinot Noir, Savagnin, and Gouais Blanc are old varieties, believed to be closely related to Vitis sylvestris, and found in the lineage of many common European grape varieties. Most crossings arose naturally, but a few well-known examples are products of breeding. The teinturier grape Alicante Bouschet, whose durability and deep color made it popular with home winemakers during Prohibition, was produced by crossing Petit Bouschet, also an intensely colored teinturier with thick skins, with fruit-forward Grenache. Müller-Thurgau, once a very important variety in Germany, was produced from Riesling and Madeleine Royale in an attempt to develop an earlier-ripening grape with Riesling-like aromatics. South Africa’s signature grape, Pinotage, was bred to combine the elegance of Pinot Noir with the hardiness and productivity of Cinsault.

From an evolutionary perspective, vinifera grape varieties are organized into three proles, indicating the primary center of their cultivation, evidenced by their physical characteristics. Proles pontica, which includes Zinfandel, Furmint, and Vermentino, is native to the Aegean and Black Seas and has more jagged leaf blades; white hair on the underside of the leaves; mid-sized clusters; and small-to-medium, round berries. Proles occidentalis is native to Western Europe and includes most international grape varieties, such as Cabernet Sauvignon, Chardonnay, Pinot Noir, and Riesling. Occidentalis has convex leaves; small, compact bunches; and small, round berries. Proles orientalis is native to the Middle East, Iran, and Afghanistan and has large leaves, bunches, and berries with an oval shape. Muscat, Cinsault, and most table grape varieties are examples.

Grape varieties differ significantly from one another, both in terms of wine flavor and environmental adaptations, as a result of their unique genetics. Every variety is hardwired to produce different amounts of flavor, color, and tannin. The chemical pathways that create each of these may be upregulated, where the production of a compound is increased, or downregulated, where that production is decreased, in response to the environment. For example, grapes under water stress will produce more tannin than those with an ample water supply, even after accounting for the difference in berry size. Varieties also exhibit different behavior. Some go through budbreak a couple of weeks earlier than others, some require more heat accumulation in order to achieve ripeness, and varieties differ when it comes to yield potential, vine vigor, and tolerance to environmental stressors.

The grape varieties are usually divided into red (or black) and white grapes, though pink (or gray) versions exist as well, such as Gewürztraminer and Pinot Gris. White grapes can be further characterized as aromatic, partially aromatic, and non-aromatic, primarily resulting from the grape’s propensity to form monoterpenes, compounds responsible for flavors of rose, lychee, and orange blossom. Red grapes differ in their amount of color and its hue. In both cases, levels of acidity and tannin vary, and each grape has a unique flavor profile. 

Clones

Clones are variants within a grape variety that differ slightly in terms of morphology or behavior. Grapevines are prone to mutations that arise from errors during cell division, and the genetic variation that results is the major source of clonal differences. Mutations can affect a single bud, leaf, or flower. When a bud is affected, the single resulting shoot may bear some distinction from the parent vine. Cuttings taken from this shoot would constitute a unique clone that may differ from the parent plant in terms of grape color, ripening dates, yields, berry and cluster morphology, and flavor characteristics. Viral infection also influences gene expression and is another source of clonal variation. The Gingin clone of Chardonnay that is popular in Western Australia, for example, was confirmed to have grapevine leafroll virus, believed to be responsible for some of its positive attributes, including low yields. When clonal selection is performed in a nursery, virus-infected vines are heat-treated to remove the virus before they are propagated and distributed. 

Old varieties typically exhibit more clonal diversity. Pinot Noir is thought to be at least 2,000 years old, and as a result, many diverse clones exist. As mutations accumulate over time, significant changes may result in the mutant being renamed as an entirely different variety. Pinot Gris, Pinot Blanc, Pinot Meunier, and Pinot Teinturier are considered by many to be separate varieties, but each is technically a clone of Pinot Noir. Similarly, the highly aromatic, pink Gewürztraminer is a mutation of Savagnin Blanc. 

Hybrids

Hybrid grape varieties allow for viticulture in environments where grapes would not otherwise grow successfully. In America in the early and mid-1800s, vinifera was interbred with native American grape species like Vitis labrusca and Vitis aestivalis that are better adapted to the cold winters and humid, disease-prone summers of much of the Eastern United States. The resulting hybrid varieties include Clinton, Concord, Catawba, Delaware, Herbemont, Isabella, Niagara, Noah, and Norton. While some of these are used for wine, many are considered better suited to fruit juice and jam on account of their foxy flavors. Hybrids tend to be high yielding, and the resulting wine is generally regarded as inferior to that of pure Vitis vinifera. 

After the introduction of phylloxera and powdery and downy mildews to Europe, French researchers looked to hybrids to instill pest and disease resistance until better treatments were found. Beginning in the late 1800s, a large number of French hybrids were generated, including Baco Noir and Blanc, Chambourcin, Chancellor, Couderc Noir, Plantet, Villard Noir and Blanc, Seibel, and Seyval Blanc. These played an important role in European wine production from the late 1800s until the mid-1900s. By the end of the 1950s, hybrid grapes covered one-third of France’s vineyard area. Subsidies encouraged producers to replant vineyards to vinifera grapes, and by the late 1980s, hybrid varieties accounted for only 3% of European production. Today, most hybrids are not permitted by the EU for PDO wine production, though exceptions exist. The German Rondo and Regent, used for their disease resistance and cold tolerance, are most common.

French hybrids like Vidal Blanc, Vignoles, Chambourcin, Seyval Blanc, and Maréchal Foch are more typical in vineyards in Eastern and Midwestern North America, along with newer varieties like Cayuga White, Chardonel, Frontenac, and Traminette, which were bred to withstand winter freeze. Japan’s signature grape, Koshu, is a vinifera-dominant hybrid crossed with the East Asian species Vitis davidii. Hybrid grapes are considered by some to be more sustainable, since many are disease resistant and require significantly less use of fungicides.

Rootstocks

When a vine is grafted, some characteristics of the rootstock are conferred to the scion. While rootstocks were first developed for phylloxera resistance, today, they have other adaptations that may be beneficial to a vine, as they differ in terms of vigor, drought tolerance, resistance to pests and diseases, and adaptations to various soil conditions.

Most rootstocks are hybrids of non-vinifera grape species, especially North American varieties. Three species are frequently encountered: Vitis riparia, Vitis rupestris, and Vitis berlandieri. Other examples include Vitis champinii, Muscadinia rotundifolia, and Vitis solonis. Offspring of these species usually demonstrate characteristics inherited from both of their parents. By knowing the general attributes of each, the behaviors of their offspring can be better understood.

• Vitis riparia is native to riparian areas, or those alongside rivers, throughout much of eastern and central North America, where it grows up trees. Because its native habitat is near water, riparia forms shallow, fibrous roots and is not drought tolerant. Riparia induces low vigor and early ripening in the scion and confers phylloxera resistance. It is easy to propagate but does not do well in lime soils. Riparia Gloire is a pure riparia rootstock.
• Vitis rupestris is native to the American South. A shrubby vine that thrives in rocky creek beds and nutrient-poor areas, it grows extensive roots, resulting in drought tolerance in deep soils. Rupestris is vigorous and will induce large canopies in the scion when planted on fertile soils. It is resistant to phylloxera and somewhat tolerant of nematodes and viruses, so it may result in less virus expression. Rupestris is easy to propagate. St. George is a pure rupestris rootstock.
• Vitis berlandieri is native to deep limestone soils in Texas and a good choice for use on alkaline soils. Berlandieri develops deep roots and confers some drought tolerance. It induces later ripening and has variable phylloxera tolerance. Berlandieri vines will not root from dormant cuttings so must be bred with another vine in order to be commercially viable.

Climate

The environmental conditions within the vineyard play an important role in shaping wine expression. This phenomenon has been described as terroir. While terroir has been interpreted literally to refer to vineyard soils, most definitions have expanded to encompass the influences of climate, topography, human practices, and sometimes other external biological factors such as microorganisms and virus. Whatever the precise definition, terroir is broadly understood as the elusive quality that gives a wine a sense of place and makes it a more intriguing, unique product.

The vine’s environment fosters its growth and development. Because a vine is not able to move, it must instead adapt. These adaptations often manifest themselves as differences in fruit characteristics. As an example, water-stressed vines will develop a smaller canopy that provides less shade to the fruit. Along with a host of other differences in fruit composition, berries that develop in the sun will produce more “sunscreen” phenolic compounds. Fruit ripening dynamics, and the amount of sugar, acid, tannin, and flavor, are all impacted by environmental conditions. It is for this reason that wine is often said to reflect the place in which it’s grown.

Climate refers to the patterns and overall amount of heat, sunlight, precipitation, and wind that characterize a region. A related and often confused concept is weather, which describes these properties over a short period. Climate is the long-term average of weather over time. It is often separated into three spheres of influence: macro-, meso-, and microclimate. Macroclimate describes the climate of a larger region, spanning tens to hundreds of miles. While not well defined, mesoclimate identifies a smaller area, a single vineyard or a region that perhaps spans tens of miles and might be impacted by local geographical features like smaller bodies of water, topography, and soil conditions. Microclimate describes the environment directly around the vine and fruit. While this is influenced by the vineyard site, human practices such as trellis systems and canopy management play an important and often underappreciated role in shaping the environment. 

Climate Classifications

Climate classifications consider patterns of temperature and precipitation to give a high-level synopsis of weather patterns and potential hazards. They are a convenient means of comparing regions to one another. While grapes are often associated with Mediterranean climates, some wine regions are better described as maritime, continental, or even subtropical. Mediterranean and maritime climates are moderate, with a small range between summer and winter temperatures. Continental climates have a more dramatic temperature swing throughout the year and experience the classic four seasons. Mediterranean climates have wet winters but receive little rain during the growing season, while maritime and continental climates receive rain year-round. Burgundy, Austria’s Wachau, and Mendoza are typically considered continental; Bordeaux, New Zealand’s Hawkes Bay, and Oregon’s Willamette Valley are maritime; and Tuscany, the Barossa Valley, and Stellenbosch, South Africa, are best described as Mediterranean. While labels are convenient, it’s useful to think of these classifications as a spectrum, with most regions falling in between specific definitions.

Vines are temperate plants and require a dormant season prior to budbreak. As a result, climates without sufficiently cold winter temperatures are not suitable for wine grape production. Tropical climates, for instance, have little temperature variation throughout the year and are not suited to wine grapes, but there are subtropical regions where grapegrowing occurs, including parts of eastern Australia, Madeira, and the Canary Islands. Often, grapes grown in these climates are made into fortified wines, where the effect of the vineyard site is arguably less important than the impact of winemaking. 

In the EU, wine regions are classified into zones depending by climate, and certain practices including chaptalization, acid adjustments, and minimum potential alcohol requirements are governed by zone. Germany, the Loire, Champagne, Alsace, and Austria belong to Zones A and B, which are permitted to enrich wine by 3% ABV and deacidify, but not acidify. Portugal, Southern Spain, Southern Italy, and parts of Greece belong to Zone CIIIb. They may acidify, but not deacidify, and enrich to a lesser extent. 

The Köppen-Geiger climate classifications divide regions into five main groups—tropical, dry, temperate, continental, and polar—and then further into subgroups based on temperature and precipitation patterns. Under this scheme, most winegrowing regions are categorized as temperate. While this is a very precise and well-defined index, it is seldomly referenced in regard to wine.

Environmental Factors

Differences in climate can be distilled into a few key properties that are fundamental to a vine’s development: heat, light, water, and nutrients. Without sufficient amounts of each of these, a vine will not be fruitful and, in extreme cases, cannot survive.

Temperature

It has been said that temperature is the metronome of plants. Heat drives vine growth and development, and many of a plant’s metabolic processes are temperature dependent. In warm climates, vines grow and develop more quickly, and fruit ripens earlier. Vine growth occurs between 50 and 95 degrees Fahrenheit, where mid-70s Fahrenheit is optimal. At lower temperatures, vines are dormant, and at temperatures over 95 degrees, vine growth and fruit ripening may shut down to conserve water. In hot weather, the microclimate around the canopy may actually be significantly cooler than the ambient temperature, as the vine cools itself through transpiration provided that it has a sufficient supply of water. Frigid temperatures can lead to injury and even vine death if precautions are not taken. 

Temperature affects both the quality and quantity of grapes. At bloom, it impacts the number of berries that will develop in the current growing season as well as the number of clusters that form the following year. Warmer temperatures result in higher yields, and vines will develop more capacity to support the additional crop. 

Understanding a growing region’s temperature profile, which includes both the overall amount of heat and patterns of accumulation, helps growers predict which grape varieties will be most successful. Varieties differ in the amount of heat needed to ripen. It is often claimed that the best quality wine comes from marginal climates where heat accumulation is just sufficient to ripen the grapes, with classic illustrations being Pinot Noir in Burgundy and Riesling in the Mosel. Flavor profiles are impacted, too. Warmer climates tend to yield fruitier wines, with higher alcohol, lower acidity, and softer tannins, but overripeness is a risk if harvest occurs later in the season. In cooler climates, wine may have lower alcohol, higher acidity, more astringent tannins, and fresh fruit and savory flavors; in some years, however, wines may be underripe and lacking flavor. 

Heat indices are used to guide varietal selection and to compare climates, estimating the amount of heat that accumulates throughout the growing season as the product of temperature and time. In the United States, the Winkler Index is frequently used to categorize viticultural areas with similar accumulation of “growing degree days” from April 1 to October 31. A region’s degree days are calculated by taking the average daily temperature minus 50 degrees Fahrenheit from every day within this range and summing them. The correction of 50 degrees is used to acknowledge that below this temperature, little shoot growth takes place. The Winkler Index is easily employed, but because it does not account for day length, it is not applicable to all regions. Elsewhere, the Huglin Index, which accounts for latitude, is more common.

While heat summation is a useful metric, the pattern of heat accumulation is also important. A moderate climate with a long growing season may experience the same overall heat accumulation as a warmer climate that has a short season, but each will impact the fruit differently. Two important concepts related to heat accumulation patterns are continentality and diurnal shift. Diurnal shift describes the difference between day and nighttime temperatures. In warm climates, a large diurnal shift is often thought to be important for wine quality as it seems to preserve acidity and flavors. In marginal climates, warm nights may assist in developing acid and flavors.

Continentality is the difference between summer and winter temperatures. Continental climates have wide temperature swings throughout the year and are more prone to spring and fall frost. Continentality can be assessed by comparing the average temperature during the warmest and coolest months of the year.

Light 

Sunlight is essential for plant growth. Light in the canopy fuels photosynthesis, which drives plant growth and development and creates sugar that facilitates fruit ripening. The number of sun-exposed leaves on a vine will determine its photosynthetic capacity, where more leaves results in a higher capacity for development, as well as greater water use. About 12 to 16 leaves are required to ripen a cluster. 

Metered, or dappled, sunlight improves fruit quality and quantity. Shaded buds are less fruitful, but ample light exposure on the shoots increases yields in the following year. Shaded berries ripen more slowly, while berries with direct light exposure can reach high temperatures, which may interfere with ripening. During a heat spike in 2017, one Napa Valley vineyard observed temperatures in excess of 140 degrees Fahrenheit in sunlit berries. Though light determines the rate of photosynthesis and therefore sugar accumulation in the fruit, other features of ripening, like acid degradation and tannin ripening, may be more tied to temperature.

Sunlight is typically considered important for flavor development. Light stimulates the production of phenolic compounds, like anthocyanin and tannin, that are considered key for red wine quality, as well as 1,1,6,-trimethyl-1,2-dihydronapthalene (TDN), the petrol flavor observed in aged Riesling. It also encourages the breakdown of pyrazine, the green bell pepper flavor associated with grapes such as Cabernet Sauvignon and Sauvignon Blanc. While sun exposure upregulates the production of certain flavor compounds, the increase in temperature can result in flavor loss, acid degradation, and sunburn. 

The duration of sunlight during the day (sunshine hours) and its intensity influence vine and fruit development. Vitis vinifera is said to require at least 1,250 sunshine hours to ripen fruit. Higher-latitude regions have longer days and receive more sunshine hours, while the sunlight intensity is greater nearer to the equator. Sunlight intensity also increases with elevation, but cloud cover, pollution, and smoke can reduce the amount of sunlight that reaches the vine. 

Water

Too little water can stunt growth and development, limit yields, and delay ripening. Under severe water stress, vines close their stomates to conserve water, halting photosynthesis and plant function. Extreme drought conditions result in defoliation and, eventually, vine death. Yet wet conditions can result in excessive yields and slow ripening and encourage the vine to produce a big, vigorous canopy. 

Timing is also important. An adequate amount of available water is desired early in the season so that shoots reach their full height prior to veraison, when berries change color. Once berries have formed, mild water stress helps to maintain a moderate berry size and promotes the production of phenolic compounds, which are considered integral to red wine quality. Near the end of the season, water deficit can cause dehydration, but rain near harvest can cause berries to swell and split, resulting in dilution and increased disease pressure. Late-season rain frequently reduces wine quality.

The amount of water available to the vine depends on soil conditions. Soil has a limited capacity to hold water. Heavy rainstorms can deposit a lot of water, but it may not be accessible to the vine, as some is lost through drainage or run-off. On deep soils, well-developed and deeper root systems allow a vine to source water from a larger volume of soil; shallow soils are more limited in their capacity. 

The impact of water availability on vine and fruit development, and especially on wine quality, is one of the most important topics being studied in viticulture today. By providing just enough water when the vine needs it, viticulturists hope to improve wine quality and conserve precious resources.

Wind 

Along with windbreaks, other protective measures can be taken in windy climates. In Provence and the Southern Rhône, the vineyard rows may be planted parallel to the prevailing wind, with vines trained low to the ground, in order to minimize damage. In parts of coastal California, some producers have observed that rows planted perpendicular to the wind will “self-shelter,” resulting in higher sugar accumulation. Regions like Greece’s Santorini and Lanzarote in the Canary Islands have developed novel vine training systems for wind protection.

Geographical Factors

Latitude 

Wine grapes generally grow between 30 and 50 degree in latitude. In lower latitudes, the vines don’t experience a dormant season, while higher latitudes are often too cold for grapes to attain ripeness, or vines may be threatened by winter freeze. Both temperature and sunlight intensity are generally higher for regions closer to the equator. Those regions further from the equator often have shorter growing seasons but longer days, which accelerates growth and development. Marginal climates may also rely on other influences that increase their viability. For instance, higher latitudes often rely on warming from bodies of water, favorable orientations, and warm air currents, while lower latitudes may benefit from cooling influences like high elevation. 

Hills & Mountains 

Hills and mountains can result in significant climatic diversity. The first relevant factor is altitude, which tends to reduce temperature but also increases sunlight intensity. Roughly, for every 300-foot gain in elevation, the temperature will decrease by about 1 degree Fahrenheit, and for every 1,000-foot increase, there is a 2% increase in sunlight exposure. Because cold air sinks, lower-elevation bowls trap cold air and may be more frost prone. Gravity causes soil and water to run downhill, so the bottom of the hill typically has deeper soil and more available water. Mid-slope sites are often considered best for wine quality, as they seem to have an ideal balance of soil and water conditions, along with favorable airflow to prevent frost and disease. 

Some parts of a hill are warmer and sunnier than others. Slope, or the degree of incline, is an important factor. In Côte Rôtie, inclines can exceed 55 degrees. Vineyards in the Mosel reach 70 degrees—these are considered the steepest in the world. While the sun’s position changes throughout the day and year, steeper slopes will intercept the most sunlight on average and tend to be earlier ripening. (Solar panels are positioned at an angle for the same reason.) In Burgundy, grand cru vineyards are often located mid-slope, on the steepest and earliest-ripening part of the hill.

Aspect, or orientation, is the cardinal direction that the vineyard faces. In the Northern Hemisphere, south-facing vineyards intercept the most sunlight during the day, are warmer, and usually ripen earlier than north-facing vineyards, which tend to be the coolest sites. East-facing vineyards get more morning sun, reducing early morning humidity and thus minimizing disease pressure, while west-facing vineyards are exposed during the most intense part of the day, making them more prone to sunburn. Historically, south- and southeast-facing vineyards were preferred, as these conditions facilitate ripening. Mountain ranges tend to have a windward side that experiences more weather and precipitation, with a leeward side that is drier and more protected. Alsace and Mendoza, for instance, are both located in the rain shadows of nearby mountain ranges and receive relatively little precipitation.

Bodies of Water

Many historic winegrowing regions are situated along bodies of water, as this positioning provided a means of transport as well as groundwater or a source of irrigation. As with hills, where a vineyard lies in relationship to an ocean, lake, or river will affect its climate. Water has a large heat-holding capacity and changes temperature slowly. As a result, proximity to bodies of water results in a more moderate temperature range on both a daily and annual basis. Water can also reflect sunlight onto the vines, helping vineyards to ripen earlier. 

Air currents that move along water can bring cold or warm air into a region and create fog and mist that reduce the amount of sunlight reaching the vines. Viticulturally important examples include the cooling Humboldt Current off of Chile and Benguela Current in South Africa. The Gulf Stream warms much of Northern Europe, allowing grapes to ripen in locations where they otherwise might not. 

Climate Change 

The wine business tends to be fixated on the weather due to its profound impact on vintage variation. Because of this, grapes are considered a more sensitive barometer of climate change than other crops. The industry has collected detailed records that illustrate changes over the past 50 years, including in heat accumulation, temperature extremes, and rainfall patterns. In some areas, drought and fire are more rampant than in the past. Changes in climate could redefine quality potential and wine style in classic regions throughout the world. Thus far, they have benefited some areas. Southern England was once considered unsuitable for grapegrowing but is now showing promise for sparkling production. Classic regions in Italy, France, and Germany are producing great vintages more consistently.

Alongside any effects of climate change, significant adjustments in viticultural practices over the past 50 years have also played a role in shifting wine styles. Not long ago, many regions struggled to adequately ripen grapes. As a result, viticulture developed practices specifically intended to accelerate the ripening process, and these were widely adopted. Producers developed more efficient canopy architecture, reduced yields, irrigated less, adopted earlier-ripening clones and rootstocks, and removed diseased vines that delayed ripening. The effect of these changes on grape ripening and wine style should not be underestimated.

Today, producers are looking to viticultural practices to slow ripening. Cooler sites that were historically less desirable, like those with a north-facing aspect, may be preferred in the future. In some cases, producers are even looking to new varieties; in Bordeaux, a proposal to allow seven new grape varieties in AOC wines was put forward in 2019.

Weather Hazards

Frost

Spring frost can kill young shoots, and while new shoots will often replace the lost ones, their development is delayed and they are typically less fruitful. Frost that occurs in the fall prior to harvest will kill the leaves, which prevents the vine from being able to ripen fruit further. In this case, the fruit will not improve and should be picked right away. These frost events are often the result of an inversion layer, where cold air near the ground is trapped under warmer air.

There are several means of frost mitigation:

• Site selection: Because cold air settles into areas of low elevation, especially bowls that have no way of draining, early-budding (and therefore frost-prone) varieties should be avoided on these sites.
• Air circulation: Cover crops and plants growing on the vineyard floor should be mowed short prior to frost season to allow for better air circulation.
• Sprinklers: Overhead sprinklers can be used to warm the surface of the vine by a few degrees. As water freezes, it releases heat, so as long as water is constantly applied during a frost event, the temperature will remain just above freezing.
• Fans or helicopters: These disrupt the inversion layer to warm the environment.
• Pruning methods: Vines may be pre-pruned, where spurs are left long, or late-pruned. This encourages sacrificial buds to push early in the season, knowing that a later pruning will remove damaged tissue.

Winter freeze can cause damage to dormant vines if temperatures fall below 5 degrees Fahrenheit. The methods described above only increase the temperatures slightly so are insufficient for protecting against winter freeze. Most vinifera vines can survive until 0 degrees Fahrenheit, but much below this, they risk death. In regions where winter freeze occurs, cold-tolerant varieties like Riesling and select hybrids may be planted. Otherwise, vines are buried each year for insulation and uncovered the subsequent spring. Recently, some producers have begun covering the vines in geothermal, geotextile blankets as an alternative means of freeze protection.

Hail

Hail regularly causes major localized damage in susceptible regions, including parts of the Loire Valley, Burgundy, Bordeaux, Piedmont, and Mendoza. Its impact on a particular growing season is dictated by the intensity of the event and the phenological stage of the vine. Hail can remove entire shoots and severely damage fruit as well as leaves, reducing the canopy’s capacity to support fruit ripening. Some regions have started using netting to protect the vines from hail. Another method is to fire hail cannons or rockets into the air, disrupting hail formation.

Drought

Many vineyards that thrived in the past now struggle due to lack of water. As with many weather hazards, site selection is key to limiting drought risk. Where it is possible, irrigation can help mitigate damage. Many wine regions in the EU that did not previously permit irrigation, including Bordeaux, Burgundy, Barolo, Barbaresco, and Montalcino, now allow it when faced with drought conditions, though additional restrictions may apply. Drought-tolerant rootstocks such as St. George, 110R, and 140R can also be used to better adapt the vine to its environment.

Risks of warm, dry environments include sunburn, which results in caramelized flavors, and dehydration, which concentrates sugars and acid in the fruit and can lead to raisinated flavors. Except in extreme cases, the risk of dehydration is typically not until later in the season, when the fruit has begun softening. Maintaining a protective canopy can help reduce the risk of sunburn, and where this is not possible, growers are increasingly using shade cloth, or fabric that is hung in the fruiting zone after veraison, to protect the fruit from dehydration and sunburn later in the season. In extreme heat events, sprinklers or misters might be used for evaporative cooling. In Australia, some producers apply a clay-based “sunscreen” to the fruit and canopy for protection.

Fire 

Forest fires that occur near wine regions are a growing problem. While vineyards often act as firebreaks and aren’t likely to burn themselves, smoke can be taken in through pores in the grapes or leaves and then translocated to the fruit any time after fruit set. This will taint the wine with an unpleasant, smoky flavor. The West Coast of North America, much of Australia, and parts of Portugal and Spain have all suffered damage from smoke in recent years. Although researchers are currently devoting attention to this topic, currently, there is no successful form of mitigation in the vineyard.

Soil

While a region’s weather varies from year to year, soil is reasonably stable. In this sense, it is the most enduring aspect of a wine’s sense of place. The basic function of soil, with respect to the vine, is to anchor it and provide it with water and nutrients. Soil conditions determine how much precipitation actually reaches the vine, since different soils absorb and hold water differently. Most critical to wine quality, soil characteristics impact vine vigor, which is driven by the availability of water and nutrients. 

Vines grown in favorable soil conditions will have deep roots and balanced vigor and are able to adapt to wet and dry conditions more easily. Free-draining soils with limited but adequate water and nutrients are best for wine quality. Highly fertile soils induce too much vigor and are typically avoided, as are soils with toxicities, including high salt or aluminum concentration. 

Popular Geology

As the notion of terroir has been popularized, vineyard soils have become a topic of interest for many wine enthusiasts. Wine descriptions often include information on rocks and soils found in the vineyard, such as their composition, geological age, and origins. 

Vineyard soils are often described by the qualities of their underlying bedrock. All rocks are classified into three types as determined by the geologic forces that formed the parent material:

• Igneous rocks like granite are formed from cooled magma and tend to be strong, resistant to erosion, and non-porous. Volcanic rocks are a type of igneous rock formed from lava. Basalt is a volcanic rock that breaks down to form highly fertile clay soils.
• Sedimentary soils are formed from weathered rocks carried by wind or water and deposited in layers. Limestone, chalk, shale, and sandstone are examples. The characteristics of these soils depend on what they’re made of and how strongly they’ve been cemented together.
• Metamorphic rocks are igneous or sedimentary rocks that have been subjected to heat and pressure. The category includes slate, schist, and gneiss. These rocks may be crumbly and friable or very hard, depending on the forces that shaped them and the underlying rocks’ composition.

While these types of rocks are often encountered in wine studies, the information they provide is limited, since these convenient classifications often combine dissimilar soils within a single category. Two vineyards with similar bedrock may have entirely different soils overlaying them. For example, a vineyard with granite bedrock could be overlaid with deep sandy soils or very thin soils. From a viticultural perspective, soils are characterized instead by their physical and chemical characteristics, since these properties determine the amount of water and nutrients available to the vine. 

A soil’s geological age, which generally refers to the time period when the underlying bedrock formed, is another property that is frequently cited in wine literature. The Kimmeridgian soils developed during the Jurassic Period from marine sediments, for example, are often noted, as they famously appear in Chablis, the Aube region of Champagne, Sancerre, and Southern England. Just as there is huge diversity in soil today, the sediments laid down during the Jurassic Period were not homogenous; to describe a soil by the time its parent material was formed, while interesting, is not terribly meaningful.

Physical Properties

Great wines are made from grapes grown on a range of soil types. Within individual regions, producers frequently attribute wine qualities to the rocks found in their vineyard, but more generally, rock type does not appear to be well correlated with wine’s composition or attributes. While different soils clearly contribute to creating distinct wines, many of the differences ascribed to rock type are actually the result of physical attributes of the soil. 

A heterogenous mixture, soil is comprised primarily of minerals, water, air, and a small portion of organic matter. It’s made from weathered rock, plant material, and soil microbes. Soil’s formation is said to depend on five factors: the parent material, climate, topography, organisms, and time. The hardness of the parent rock will determine how easily it is broken down into soil. Warm, wet conditions will accelerate the weathering process, and the erosion that occurs by water and wind will be shaped by an area’s topography. Rocks and organic matter are broken down by the action of soil microbes and plants’ roots. This occurs slowly: it takes at least 100 years to form an inch of topsoil. Because soils are also transported by erosion, wind, leaching, and the action of rivers and glaciers, vineyards that share a common bedrock composition can have very different soils overlaying them.

Soils are organized into layers of sediments called horizons. Topsoil, or horizon A, is the outermost layer and ranges in depth from a few inches to a few feet. The composition of soil in this layer least resembles the composition of the underlying rock, since it has often been deposited from elsewhere. The topsoil contains most of the soil’s organic matter, worms, and microbes. Humus, an important topsoil constituent, is nutrient-dense organic material that holds water and nutrients in the soil, reduces erosion, and helps avoid soil compaction. As rainwater moves through the soil, it leaches smaller particles and nutrients downward. As a result, horizon B, called the subsoil, is less porous, contains a higher proportion of clay, and has better water-holding capacity than the topsoil. Horizon C, or the substratum, may consist of friable rock, and few if any roots are found here. Bedrock, which lies underneath the soil, is not soil at all but the outer layer of the earth’s surface. The manner in which roots navigate this complex layering of soil strata dictates the amount of water and nutrients the plant can access all year long. 

Soil is a reservoir of water for plants. After a rain event, water is lost through run-off, drainage, evaporation, and plant use. Several attributes influence how water drains and is stored in the soil to be used in the future. Soil depth, or the distance from the soil surface to the bedrock or another impenetrable layer, limits a vine’s rooting depth, which determines the deepest soil that the vine can access. (Roots may, however, be able to penetrate small cracks in friable bedrock.) Deep soils allow roots to access water from greater depths and provide the vine with more water throughout the growing season since the roots are in contact with a larger volume of soil. Because grapevines can develop deeper root systems than most other plants, on these soils, they can access water few competing plants are able to reach. Shallow soils can flood easily and have less available water than deeper soils; they require regular additions of water, sometimes through irrigation, to meet the vine’s needs. Shallow soils are generally not suitable for dry-farming except in climates that receive regular precipitation. Where an impenetrable layer, such as a hardpan, limits the rooting depth, the soil may be ripped prior to planting. Ripping involves dragging a large steel implement through the soil to break up an impenetrable layer. If shallow soils overlay bedrock, ripping is not possible, although modern heavy machinery, including excavators and pneumatic rock breakers, has allowed viticulture to extend into otherwise unusable land.

Two related concepts are key to healthy plant growth: porosity, or the amount of open space in the soil, and permeability, which describes the ability for water, oxygen, and roots to pass freely. These factors allow for drainage, water storage, root growth, and aeration, which are essential for healthy roots and soil microbial populations. Growth will be limited in waterlogged and non-porous soils. Porosity is governed by soil structure, an attribute that describes how soil particles aggregate, or form small clumps, and how easily these clumps crumble. Large pores between soil aggregates increase the porosity of well-structured soils and ensure that water on the soil surface is absorbed. These soils are better able to resist erosion and compaction. A moderate humus content helps the soil stick together, which improves the soil’s integrity. By increasing soil organic matter through the addition of compost and usage of cover crops, it is possible to build better structure in the soil.

Sidebar: Compaction

Vineyard soils are prone to compaction due to the repetitive use of tractors and other heavy equipment in the vine rows. Compaction destroys porosity, and limited infiltration of water and oxygen in these soils inhibits root growth. To avoid compaction, producers try to avoid unnecessary tractor passes and may use tillage to aerate the soil in conjunction with cover crops, which break up compacted areas with their roots.


Soil texture also influences porosity and permeability. Texture, referring to the size of soil particles, includes sand, silt, and clay, where sand particles are largest and clay smallest. Loam is a mixture of the three types and falls on a spectrum depending on the proportion of each component. Soils also contain rocks of different sizes, including gravels, pebbles, cobbles, and boulders. Rocks do not contribute water or minerals to the vine, but they increase drainage and limit erosion. They are generally considered beneficial for vine roots, when not overwhelming in proportion.

Sandy soils are sometimes called light soils, while clay soils are described as heavy, a reference to their superior water-holding capacity. Water is held in the soil by sticking to the surface of soil particles and through capillary action (the attraction of water molecules to each other and other substances), which is more effective with smaller pores like those found in clay. Because clay particles are small, they pack more tightly together and have more surface area per volume. Soils heavy in clay content have better structure than sandy soils but can be prone to water logging and tend to harbor higher populations of phylloxera.

As a result of their lesser water content, sandy soils warm up faster than clay soils, which initiates budbreak sooner and accelerates ripening. In a cool or wet vintage, sandier soils may perform better, while in a warm and dry year, soils with a higher clay content may be preferred. Parasitic nematodes are particularly fond of sandy soils.

Loam soils are considered ideal for vineyards, since the combination of particle sizes achieves the ideal balance of drainage, provided by the sand, and fertility, provided by clay, that is desirable for balanced vine growth.

Chemical Properties

While wine style is clearly influenced by the physical factors that dictate water availability, except in the case of nutrient deficiencies, few differences in wine can be attributed to a soil’s chemical composition. 

Rocks are made of minerals like quartz, mica, feldspar, gypsum, calcite, and flint. These minerals do not make their way into the glass directly; rather, the vine roots take up only small ions, including the 17 mineral nutrients that are described below. (Note that minerals and mineral nutrients are distinct from one another, though frequently confused.) While the weathering process releases a small amount of mineral nutrients from the soil, most of the nutrients supplied to the vine come from organic matter and fertilizers. Current understanding of rock chemistry suggests it does not play an important role in soil chemistry, with one important exception: calcareous soils are strongly alkaline. 

Soil pH

The pH of soil is its most important chemical property. pH is a scale of acidity that ranges from 0 (very acidic) to 14 (very basic), with water considered neutral at a pH of 7. Technically, pH is a measure of the hydrogen ions, or protons, dissolved in a solution, where more acidic substances have more protons. pH is a logarithmic scale, which means that a pH of 6 has 10 times the amount of protons as a pH of 7.

A soil’s pH influences the mineral nutrients that are available to the vine. Nutrients are stored by adsorbing, or sticking, to soil particles. Positively charged nutrients are attracted to soil particles, which are largely negatively charged. Soil particles have a limited surface area to hold nutrients, described as the cation exchange capacity (CEC). Larger particles like sand have less total surface area per volume and are less nutrient dense. Clay soils are rich in nutrients, but because the nutrients are bound more tightly, they are less available to the vine. Soil organic matter also increases CEC.

Nutrients compete for space on the CEC, so too much of one nutrient can induce a deficiency in another. In acidic soils, protons take up too much space on the CEC, and as a result, some nutrients are less available in low-pH soils. Acidic soil induces phosphate deficiency, while alkaline soils can induce iron deficiency. Along with soil texture, pH has a significant influence on the availability of nutrients. 

pH also influences which plants will grow. Most rootstocks are not well adapted to high pH, so lime-tolerant rootstocks, often Vitis berlandieri based, must be used. This is important to recognize, since it is difficult to separate the influence of rootstock from that of soil pH.

Agricultural soils become increasingly acidic over time, which can degrade soil structure and disrupt microbial communities. As nutrients are leached from the soil, protons take their place on the CEC. The decomposition of organic matter and respiration of roots release carbon dioxide, which forms carbonic acid in the soil. Additionally, the use of ammonia-based fertilizers increases acidity over time. A farmer may amend soil acidity through liming, which is the application of limestone, dolomite, or lime (calcium hydroxide), to neutralize the topsoil. Typically, this occurs when a vineyard site is being developed, but these materials can also be applied along with compost in an established vineyard to maintain a desired soil pH. Soil organic matter helps buffer against change in pH.

Soil Toxicities

Dissolved salts like sodium chloride (table salt) are toxic to plants in high concentration, as they hinder the vine’s ability to absorb water. Water follows a concentration gradient and flows from areas with less salt content to areas with more. Irrigating with water with a high salt content is one of the biggest causes of saline soils. Parts of California’s Central Coast, Mexico’s Baja region, and South and Western Australia struggle with salinity. In response, salt-tolerant rootstocks such as Ramey have been developed to adapt vines to saline conditions. Sodicity is a related concept but considers only the amount of sodium in the soil. Too much sodium reduces soil permeability and destroys soil structure because high concentrations of sodium have a repelling effect and disperse clay particles.

Vine Nutrition

Grapes have relatively low requirements for water and nutrients, as far as agricultural plants are concerned, so they may be cultivated on soils considered unsuitable for other crops. Yet deficiencies can limit growth and development. Soil fertility refers to the ability of the soil to provide nutrients. Starving vines for nutrients can reduce yields, impede the vine’s ability to ripen fruit, and render the vine more susceptible to pests and diseases. On the other hand, excess of certain nutrients can be detrimental to quality.

Vines require 17 essential nutrients for healthy function. Carbon, hydrogen, and oxygen are supplied by water and carbon dioxide from the atmosphere, but the rest are taken up through the soil. Of those absorbed through the soil, nitrogen, phosphorus, and potassium are by far the most important, as they are essential for plant growth and development. They are considered macronutrients, along with sulfur, calcium, and magnesium, as the vine uses them in macro quantities. Boron, manganese, copper, iron, zinc, molybdenum, nickel, and chlorine are micronutrients, as the vine has less demand for them.

INSERT NUTRIENT TABLE - Macro or Micro?

Nitrogen has the most significant impact on grape quality and yields, and its availability is key to soil fertility. Insufficient nitrogen results in weak vines with short shoots and chlorotic leaves, while excess nitrogen can lead to vigorous vines with dark green canopies and reduced yields. Particularly for red grapes, the shade provided by this type of a canopy is considered negative for quality. Nitrogen-rich vines also attract pests such as leafhoppers. Plants are able to use nitrogen in the form of ammonia or nitrates. 

Potassium helps to maintains cell structure through osmotic pressure and facilitates ripening through sugar transport and deacidification. After veraison, potassium is exchanged for protons in the berries, lowering the fruit’s acidity. Potassium deficiencies can result in elevated levels of acidity in the fruit, low yields, and uneven ripening. Leaf discoloration and leaves that roll under are symptoms. Excesses can reduce fruit acidity and may induce deficiencies in other nutrients. Phosphorous is important for photosynthesis as well as energy storage and transport throughout the vine. It’s a key component of both nucleic acids and ATP. Deficiencies are relatively rare but reduce yields and cause discoloration of the leaf margin.

Nutrients are depleted from the vineyard over time as fruit and canes are removed at pruning. Certain nutrients, like nitrogen, are leachable, meaning they can be washed from the soil in groundwater runoff, while others, like phosphorus, are more immobile. Most vineyards require nutrient additions from time to time, particularly of the macronutrients nitrogen, phosphorus, and potassium (known collectively as NPK).

Producers can assess nutritional deficits through petiole sampling at flowering or veraison, taking soil samples, or observing visual symptoms. Nutrient imbalances like nitrogen and iron deficiency cause characteristic chlorosis, or yellowing of the leaves either along the leaf veins or within the leaf margin. With red grape varieties, imbalances like phosphorous and potassium deficiency may also cause reddening in the leaves due to an accumulation of anthocyanin, the same pigment that gives red grapes their color. These symptoms are easily mistaken for common diseases such as leafroll and fanleaf viruses.

Certain nutrients are mobile in the plant, and in the case of deficiency, they will be translocated from older leaves into newer ones, since the plant prioritizes the development of young leaves. Other nutrients are tied up in compounds that cannot move freely within the vine and are considered immobile. This can help with diagnosis of problems: if a nutrient is mobile, older basal leaves will show symptoms first. With immobile deficiencies, symptoms appear in younger leaves first.

Vineyard Establishment

Site Selection

Farmers have always sought the sites that produce the best wines. The phrase Bacchus amat colles, meaning “Bacchus loves the hills,” is an enduring observation from early explorations of site selection. While this process is more of an art than a science, some forethought can improve quality and save money. 

Within a region, certain sites are preferred based on their mesoclimates, the availability of water, and the rarity of adverse conditions like frost. Some sites ripen earlier than others, which may be advantageous in a cool region and less desirable in a warm one. Terrain is also a consideration. While hillside sites may be enticing, they are often more difficult and expensive to farm. Economic factors like the reputation and cost of the land and the proximity to markets, labor, and resources are considered as well. Because of the proliferation of vineyards in the past few decades, wine regions may have laws dictating if and where new vineyard land may be planted. While much of the vineyard land in Europe is already delineated, as viticulture spreads, the suitability of new sites may be evaluated by comparing their soils and climates to those of established regions.

Planting Material

In some regions, grape variety is dictated by local laws. Otherwise, the climate and intended wine style should guide the choice of varieties. election may also be influenced by factors such as personal preference, marketability, or tradition. Rootstock, where used, should be matched to the site conditions and any hazards to be mitigated, such as nematodes and high concentrations of salt or lime.

The influence of clone is generally small compared with site, variety, and rootstock. If multiple clones are available, flavor and yield considerations, ripening characteristics, disease resistance, and notoriety may guide the selection. In particular, several clones of Pinot Noir have been popularized for various flavor and ripening characteristics, including Pommard, Wädenswil, 667, 777, and 115. 

The vast majority of grapevines are grown from grafted vines with plant material obtained from a nursery. Grapevine propagation is labor intensive, and many growers are not equipped for this undertaking. Nurseries strive to provide vines that are virus free, an important assurance for a long-term investment. The downside is that nurseries are often limited in the varieties and clones that they carry.

Grapevine Propagation

Except under experimental conditions, wine grapes are almost never propagated from seed. During fertilization, DNA is recombined, so each seed produces an entirely new variety that may not possess the attributes of its parent plant. The seeds of self-pollinating vines are highly inbred and prone to recessive-type diseases; many are nonviable or non-fruiting. While they may share some similarities with their parent, vines grown from seed bear unique genetics, and it can take years to characterize a new vine’s behavior.

Instead, vines are propagated vegetatively from dormant cuttings, which are 12- to 18-inch pieces of cane taken from a parent plant. Cuttings are taken from dormant vines during the winter months and stored at low temperature until they are ready for use. Dormant cuttings of rootstock or vinifera varieties can be planted directly in the ground, or they may be grafted prior to planting. Ungrafted vines, typically rootstock selections, are sold as dormant rooted cuttings that have been grown in a nursery for a season, unearthed during dormancy, and kept in cold storage prior to planting.

Cuttings may originate from a single parent vine, called a clone, or from massal selection, where cuttings are taken from numerous vines throughout a vineyard that may have undergone small mutations. Producers who prefer clones hope to replicate the characteristics of the parent in their own vineyards. Since clones are genetically identical, they may result in a more even, easy-to-manage vineyard. A producer may instead choose massal selection for the increased genetic diversity, which could confer more disease resistance and, potentially, complexity in the wines.

Grafting is essentially the fusing of plant tissues of two different species. In the case of grapevines, grafting is typically used to join a vinifera scion to a non-vinifera rootstock. Occasionally, the variety may be changed in an existing vineyard by grafting onto established vines in the field, known as top grafting. In certain situations, this may be preferable to replanting the vineyard.

During grafting, cuts are made in both pieces of wood, allowing the vines to fit together and join like puzzle pieces. Two compatible plants with similar circumferences are connected such that their cambium, the layer of cells between the xylem and phloem responsible for wood’s increase in diameter, is matched up. Once the graft heals, the grafted vine functions as a single plant with characteristics from both the rootstock and scion. Traditionally, a number of different shapes of cuts have been used, such as a v-shaped cleft graft or an omega punch.

There are two major types of grafting in viticulture, bench and field grafting. In bench grafting, two dormant cuttings, the rootstock and scion, are joined together at the nursery, usually by machine. The scion cutting is trimmed to a few inches prior to grafting, leaving a single bud. Afterward, the graft is wrapped to provide support and stored in a warm, damp room for several months to “callus,” or heal. The graft union is then waxed, and vines are stored at cold temperature prior to planting in the spring. Grafted vines may be grown for one season in the nursery and sold as dormant bench grafts. Alternatively, the grafted cutting may be planted in a pot just after callusing, grown in a greenhouse, and sold during the same year as a green-growing bench graft, or potted vine. Potted vines are less expensive, and they mature one year earlier than dormant bench grafts. 

In field grafting, rootstock is planted in the vineyard in the spring and allowed to grow for an entire season. The scion is then grafted on top, either in the fall or following spring. Field grafting uses a technique called chip-budding, where very small pieces of cuttings containing a single bud are inserted into the rootstock. Similar to own-rooted vines, rootstock is sold as a dormant rooted cutting.

Of these options, bench grafting is easier and less expensive, and only vines that have been successfully grafted are planted. Field grafting is more expensive overall, yet the costs are spread out over two intervals. It requires skilled labor and can have a greater failure rate, but these vines have a more stable root system at the time of grafting and may have more longevity.

The choice of planting material is often inhibited by what is available locally. In the past, winemakers traveled to established growing regions and brought cuttings home with them to be used in vineyard establishment. While this practice allowed for diversification in newer growing regions, it is technically illegal in most countries and has been responsible for the proliferation of grapevine viruses all over the world. In order to import vines legally, a state-approved nursery must verify that the plant stock is pest and virus free, a process that takes several years but avoids undesirable stowaways. Foundation Plant Services (FPS) is the major US nursery used for this purpose.

Sidebar: Own-Rooted Vines

For most of history, vines were grown on their own roots. As phylloxera spreads throughout the world, ungrafted vines are becoming rare, and even in areas where phylloxera is not present, producers may still use rootstock to provide other benefits or adaptations to the scion. Some have suggested that own-rooted vines make better wines. Grafted vines are clearly changed to some extent by their rootstock, and it is not unreasonable to believe that this impacts fruit composition. Yet these changes could be positive as well as negative, and the overall effect on wine quality probably depends more on other environmental conditions.

Land Preparation

Prior to planting, land that has been used for vineyards or other agriculture in the past may be allowed to lay fallow (bare) for a couple of years or be planted with cover crops that build soil organic matter and nutrition. Soil assessments reveal a soil’s pH and any nutrient deficiencies, which are easiest to amend before planting. The land is cleared of trees, foliage, and large rocks and roots. Drainage may be improved through ripping or through the installation of subterranean drains to prevent waterlogging in low-lying spots. Earthwork is done in the spring or fall, when soils are damp but not too wet to pass equipment.

Determining a vineyard’s boundaries is one of the first steps of planning. Vineyards are typically divided into several management blocks, and thoughtful placement of the divisions between them simplifies vineyard management. Ideally, blocks are relatively homogenous in terms of variety, rootstock, soil, microclimate, and elevation. Boundaries often respect natural borders formed by topographical features, transitions in soil, and roads. A grower may choose to adapt varieties, rootstock, and vineyard architecture to the block’s natural characteristics.

Vineyard Architecture

A vineyard’s layout and trellis system design are referred to as its vineyard architecture. Orientation, or the rows’ planting direction, is a fundamental decision. A north-south orientation allows both sides of the vine an equivalent duration of sunlight throughout the day. The downside is that fruit on the west side of the vine may be overexposed to the afternoon heat. East-west rows allow the canopy to intercept the maximum amount of sunlight all day, but this will result in significant differences between the north and south side of the vine, as the south side has more exposure. Recently, northeast-southwest orientations have become popular in warmer regions, as they maximize light interception while also shading themselves during the hottest part of the day, protecting fruit from sunburn and dehydration. 

Vine spacing refers to the distance between rows as well as the distance between vines. The combination of these is called vine density, which typically ranges from 500 to 6,000 vines per acre, while the space between vines and rows typically ranges from about 4 feet to 12 feet. European vineyards tend to use higher density, with 4,000 vines per acre (10,000 vines per hectare) being common. Much of the New World uses planting densities of 1,500 vines per acre or less.

Narrow row spacing is more efficient in terms of land use but may require specialized tractors and farming equipment. High-density planting is used to limit vine vigor through competition and to maximize yields, and it is believed by some to produce higher-quality fruit. Vigorous vines, however, are better suited to wider spacing. Low-density planting may also be more appropriate for vineyards with inadequate water supply or for dry-farming, as observed in many Spanish wine regions. It can significantly reduce farming costs since less infrastructure is required and there are fewer vines to tend to per area. Efficient vineyards do not leave empty space along a vineyard row, so if wider vine spacing is used, the size of the vine is generally adjusted to fill all of the available room.

Trends in vineyard architecture are subject to the prevailing wisdom of the time. Producers often look to classic regions that they admire or to their neighbors to inform their choices. However, what works on one site, or in one region, may not be the most appropriate layout for all sites.

Planting

Planting occurs over one or two years, and once vines are in the ground, the vine requires at least two or three years to become established before any fruit is harvested. During the first year after planting, the focus is on growing healthy roots. In the next couple of years, it shifts to development of the vines’ permanent structure through vine training.

Vines are planted by hand or machine. While hand-planting is traditional, it is labor intensive. Machine planting is significantly less expensive and can have very good results; it shows a lot of promise as an opportunity for mechanization. Planting typically occurs in the spring, though vines may be planted anytime during the growing season, taking care to avoid frost before the vine has become established.

Young vines require more attention than those that are established. J-rooting, a common cause of young vine decline, occurs when vines are placed in holes with their roots bent upward. Young vines are also prone to certain fungal diseases that can result in vineyard failure if infected plant material is used. While the notion of starving vines of water to encourage deep root growth has been popularized, young vines’ root systems are not well developed, and they may require frequent irrigation. Water stress will stunt growth and ultimately shorten the life of the vine. Even in regions where irrigation is not permitted, exceptions are typically made for vineyards less than three years old. 

Growers remove weeds that can outcompete or girdle young vines and often place growing tubes around the vines to protect them from weeds and animals. During the first two to three years, any fruit that forms is typically removed to allow the vine to put maximum energy into vegetative growth. Failing to do this can weaken vines and shorten the vineyard’s lifespan. 

Vine Training

A vine’s training system is the shape and position of its permanent structures, including the trunk, cordons, canes, and spurs, and is best observed after winter pruning. The training system is ultimately determined by the cuts made during pruning in the first few years, which have a long-term impact on the vine’s shape.

The three most common vine-training systems are cordon-trained and spur-pruned; head-trained and cane-pruned; and head-trained and spur-pruned. Considerations for choosing the most appropriate system include grape variety, environmental conditions, and yield goals. Very often, tradition, which may be codified in law or local trends, will also play a role.

Cordon-Trained & Spur-Pruned

Cordon-trained, spur-pruned vines, commonly referred to simply as cordon-trained vines, can have up to four cordons attached to the trunk, described as unilateral, bilateral, or quadrilateral. Along each cordon are permanent spur positions located every few inches. As the grapevine ages, permanent wood accumulates at the base of each spur and develops into arms. Shoots grow from the spurs during the season, and during pruning they are trimmed back into spurs, so that each year, the vine looks nearly identical.

There are a number of advantages to this system, which has been widely adopted, especially in warmer regions. After establishment, cordon-trained vines are the easiest, fastest, and cheapest to prune. Shoot development along the cordon is generally very even, with a clear fruit zone. This system is also suitable for mechanization. Because these vines have more permanent wood than other systems, they store more water and nutrients and may better tolerate adverse environmental conditions. 

However, cordon-training is not always the best option. An extra year may be required before fruit is harvested to establish the cordon and spur positions. Cordon-trained vines store more reserves through the winter since they have more permanent wood, resulting in more vigor and a need for wider spacing. Spur-pruning is not appropriate for varieties that have low fertility in buds close to the cordon, such as Nebbiolo and Carmenère, since spur-pruning can reduce their yields. It is also risky on frost-prone sites. In these conditions, all buds tend to push at the same time, opening up the vine to greater loss. To minimize this risk, some growers pre-prune the vines or leave kicker canes, strategies that help minimize frost risk.

Head-Trained & Cane-Pruned

Head-trained, cane-pruned vines typically have one or two canes (though as many as four are possible) attached to the head (top) of the trunk. Guyot is a well-known variation of cane-pruning that includes one spur for each fruiting cane attached directly to the head, called replacement or renewal spurs. During the growing season, shoots form on each bud along the cane and renewal spurs. The grower selects and lays down a new fruiting cane, called the baguette in French, during pruning each year, removing the cane from the previous season. Renewal spurs ensure that there is always a good supply of canes near the head of the vine that may be retained for the coming year.

The main advantage of cane-pruned vines is that they have less permanent wood and fewer reserves, so they are less vigorous and better suited to high-density plantings. Despite their lower vigor, they are often more productive than spur-pruned vines (when grown under equivalent conditions) and may require more fruit thinning to ensure adequate ripening. Cane-pruned vines have fewer pruning cuts than spur-pruned vines; as a result, they may be less prone to fungal diseases that enter the vine through pruning wounds. Many believe that cane-pruning is inherently better for wine quality. It is used in many of Europe’s most esteemed wine regions, so it has been adopted by many producers. 

Yet there are some important disadvantages of this system. Cane-pruned vines require skilled labor for pruning, which increases farming costs, and they are not suitable for mechanization. They are more susceptible to winter freeze, because buds are located further from permanent wood, leaving them more vulnerable to damage. Due to apical dominance, budbreak and development are uneven along the cane, with uppermost buds and those located at the vine’s extremities favored. 

Head-Trained & Spur-Pruned

Head-trained, spur-pruned vines—also called bush, gobelet, or head-trained vines—have many spur positions attached to arms that form from the head of the vine. During the growing season, shoots will form at each spur position, and at pruning, the spur positions will be restored. Head-trained vines are typically found in warm, sunny growing regions with limited water availability. Much of Spain and Southern France, and vineyards with older plantings in California, utilize this training system. Head-training systems are also common with large-bunched varieties that are prone to rot, like Zinfandel and Petite Sirah, since the lack of wires and stakes prevents the clusters from becoming tangled in the trellis and damaged as the fruit develops.

Head-trained vines are the least expensive to establish and manage, since no trellis system is required, and as a result, canopy work is minimal. The initial training and pruning of head-trained vines requires skilled labor, though pruning becomes easier over time. However, head-trained vines are the least productive and not suitable for mechanization. Because all of the fruiting shoots are attached to the vine near the head, this system is prone to crowding. Head-trained vines share the same concerns of frost risk, trunk disease, and low-bud fertility as cordon-trained and spur-pruned vines.

While a number of other training systems exist, most are a variation of these basic structures, which can be adapted by leaving additional cordons, canes, or spur positions. The novel Sylvoz training system, used on high-yielding varieties and sites, is cordon-trained and cane-pruned. This results in a large number of fruiting shoots during the growing season and is an example of adapting the training system to the site and yield requirements. Champagne employs a number of unique training systems, including Taille Chablis and Vallée de la Marne, that are high-yielding and reduce the risk of frost damage.

Trellis Systems

The organization of the vine’s canopy begins with the choice of the trellis system, or the structure of posts and wires that support the canopy. A vine’s trellis accommodates its natural impulse to grow vertically and provides support for the shoots and fruit, since the vine is not able to support itself. It helps spread the shoots out more evenly, which improves airflow and light penetration in the canopy, reducing disease pressure and increasing the photosynthetic capacity of the vine. From a practical standpoint, the trellis system facilitates vineyard operations. It keeps shoots out of the vineyard row, allowing tractors and other equipment to pass. Because the shoots are organized in a predictable pattern, canopy management work is easier.

The shape of the vine training system often guides the options for trellising. The trellis typically considers the natural growth patterns of the vine. Shoots can be trained upward or downward, or they may be partially supported by a wire and then allowed to drape down. Vitis vinifera likes to grow vertically and will be devigorated if it is trained downward, whereas hybrid grapes often prefer downward growth. Large vines require more space and a more extensive trellis system, such as a divided canopy system, which has multiple fruit zones and allows the vine to spread out.

Climate, soil, variety, and rootstock must all be considered when choosing a trellis system, which will influence the vine’s microclimate. Cooler climates require more efficient sunlight interception, while sunny climates demand protection. Humidity and airflow are also important considerations. Finally, there are practical factors like cost, ease of use, and compatibility for mechanization. Simpler systems with fewer wires are usually less expensive and less labor intensive. Mechanization works best on cordon-trained, spur-pruned vines with a single “wall” of shoots. 

While a number of trellis system designs exist, it is more important to understand the concepts behind them than each individual design. While some of these trellis systems are traditional, others were designed more recently to optimize microclimatic conditions. Variations of each of these are common around the world, and many similar systems go by different names.

Untrellised Vines

Head-trained vines are typically not trellised. In sunny climates, shoots may be left to drape onto the floor, while in cooler climates, shoots may be tied to a central post for support and to allow more sunlight in the canopy and fruit zone. Untrellised vines require very little canopy management, since minimal work is required to arrange shoots. Because shoots sit on the vineyard floor, some vineyard operations, like running equipment through the rows, are more challenging. This arrangement can result in dense canopies with excessive shading and increased disease pressure, which is exacerbated by the difficulty of getting adequate spray coverage. Untrellised vines are not suitable for mechanized harvesting.

Non-Divided Canopy Systems

Cordon and cane-pruned vines have many options for trellis systems. These are broadly categorized as divided or non-divided systems, and in each case, shoots may be trained upright, or they may be allowed to hang down toward the ground.

On low-vigor sites, cordon and cane vines are often trained to one or two horizontal canes or cordons, referred to as a non-divided system, since there is a single fruit zone. Several trellis systems are commonly used for non-divided canopies. In vertical shoot positioning (VSP), the shoots are trained vertically and compressed into a single wall between several wires of support. VSP is ideal for high-density plantings. It respects the tendency of vinifera grapes to grow vertically and results in good light interception. VSP works well for lower-vigor vines, as shoots may be positioned for good airflow and coverage with anti-fungal sprays. For vines with higher vigor, the canopy may become too dense and humid, restricting airflow and harboring disease. Warmer climates that risk overexposure may require more protection in the fruiting zone. VSP is suitable for mechanization; however, this system requires additional labor to tuck shoots into the trellis. It is moderately expensive to install and operate.

Where more protection from sunlight is desired—for example, on warmer sites that are prone to sunburn—a slightly wider variation of VSP may be used, with spreader bars that open the canopy slightly. This is also good for more vigorous vines, since it allows for better airflow and sunlight penetration into the canopy and reduces crowding in the fruit zone.

A cordon-trained vine with high wire trellising (Photo credit: Jennifer Angelosante)

California Sprawl is an example of a two-wire system. In this layout, the shoots are flopped over a single higher wire that provides support and shade to the fruit zone. Two-wire systems are less expensive to install and require less canopy work than VSP. This system is compatible with vigorous canopies but may restrict airflow such that the underside of the canopy becomes humid and prone to disease. 

In high-wire systems, such as high bilateral cordon, the cordon or cane is trained along a support wire, while the fruiting shoots sprawl unsupported in all directions. It is a good low-cost option since it is well suited to mechanization and requires little canopy management, and with basic infrastructure, it is inexpensive to install. Because the fruit is located near the top of the vine, it gets good light exposure, but this system might not offer suitable protection in very warm climates. High wire systems require a tall head height, so these vines can be difficult to prune and harvest by hand. 

Divided Canopy Systems

On high-vigor sites, a divided canopy may be utilized to provide more space for the vine and avoid overcrowding. Divided canopy systems are typically quadrilateral cane or cordon-trained. The canopy may be divided horizontally, with two parallel fruit zones located three to four feet apart at identical heights, or vertically, with an upper and lower fruit zone. Many of these have an analogous non-divided canopy system. Uneven ripening is a risk of divided canopies since there are multiple fruit zones. Some producers will even harvest the different zones on different dates.

There are horizontally divided equivalents of each of the systems mentioned above. Lyre is similar to VSP, Wye is similar to California Sprawl, and Geneva Double Curtain is similar to the high-wire system. In each case, the canopy is mirror-imaged across the vine row.

Scott Henry and Smart-Dyson are unique vertically divided systems used primarily in New World wine regions including parts of New Zealand, Australia, Argentina, Chile, and the United States, as well as Spain and Portugal. Scott Henry is a quadrilateral cane-pruned system, with two canes trellised vertically and two trellised downward. This system is used for high-vigor situations where tighter row spacing is desired. While efficient, the fruit from the upper and lower fruiting zones will ripen at different times (fruit on the upper cane ripens first, another example of apical dominance). Smart-Dyson is a similar system used for high-vigor bilateral cordon vines, where shoots are trained both up and down. It is very suitable for mechanization, and the fruit on these vines ripens more evenly than with Scott Henry. Overly vigorous VSP vines can easily be retrofitted to this system. 

Other novel trellis systems are possible. Pergola, also called tendone in Italy and latada in Spain, is a classic system used on high-vigor, high-production vines in Southern Europe. Pergola systems allow workers to pass below the vines. These systems make efficient use of vineyard space, allowing maximum light interception by the canopy while also providing adequate protection in the fruiting zone. In humid areas like Rías Baixas, pergola trellising promotes airflow and reduces fungal disease pressure. Whereas the canopy of other trellis systems can be thought of as perpendicular to the ground, in pergola systems, the canopy is parallel. The high height of the fruit zone makes pruning and harvesting challenging, and this layout doesn’t easily accommodate driving equipment through the vineyard.

A Year in the Vineyard

Phenology is a term that describes a vine’s reoccurring patterns of growth and development throughout the year. Major milestones include budbreak, flowering and fruit set, veraison, harvest, and leaf fall. Except in tropical environments, grapevines fruit once per year. They spend the entire growing season establishing a canopy and ripening their fruit, and during dormancy, they survive off of carbohydrate reserves stored in the trunk and roots during the growing season.

In the Northern Hemisphere, the growing season begins with budbreak (or budburst) in March or April and ends with harvest sometime between August and November. (In the Southern Hemisphere, budbreak occurs in September or October, with harvest between February and May.) While the dates of budburst, flowering, and veraison are reasonably consistent for most varieties, with differences of about two weeks at most, a much larger span of harvest dates is observed between varieties.

Start of the Growing Season 

When the temperature begins to warm to about 50 degrees Fahrenheit, the vine begins transporting sap containing nutrients and energy stores from the roots to the buds to initiate shoot growth. This may be observed as weeping, where sap is pushed through open pruning wounds. Excessively wet conditions at this time might prevent soils from warming, stifle root growth, and delay the start of the season.

At budbreak, the dormant buds begin to “push,” and the compressed shoots stored inside begin growing. The first leaves appear, and as the shoot elongates, new leaves emerge from the shoot tip. The growth is slow at first, fueled by energy stored in the roots and trunk. Budbreak occurs according to apical dominance, where buds that are located further from the ground push first. 

After a few weeks of slow growth, the vines enter a period known as rapid shoot growth or the “grand period of growth.” During this time, shoots may increase in length by inches per day. By flowering, the shoots are typically about half of their full size. 

Flowering & Fruit Set 

Grape flowers do not resemble the common notion of a flower with petals radiating from the pistil (female flower part). Rather, grape flower petals form a cap around each flower that falls off during flowering to reveal the stamens (male flower parts). Pollen from the stamens falls onto the pistil during fertilization, and each fertilized flower turns into a grape berry. The weather during flowering is critical, as low temperatures interfere with fertilization, ultimately reducing the number of berries as well as the overall yield. Bloom typically begins six to eight weeks after budbreak and continues over a span of one to three weeks.

Shortly after flowering, during fruit set, fertilized flowers turn into berries and the yields for the season become more apparent. Under favorable conditions, roughly a third of flowers develop successfully into berries. Flowers that are not fertilized fall off.

The rapid growth phase pauses during flowering and resumes after fruit set. After set, the vine begins devoting more energy to fruit development. The berries are hard and green at first and rapidly increase in size as cells within the berries divide. Starting at set, reactions begin taking place inside the berries that will ultimately determine berry composition, and the environmental conditions around the cluster more significantly influence fruit composition. Acid, tannin, and some flavor precursors begin accumulating, and the timing of canopy management operations becomes more critical.

Veraison

Veraison is one of the most recognizable and photogenic phases of grape development, where grapes change color from green to red—or, in the case of white grapes, from bright lime green to a pale, translucent green. This occurs about four to six weeks after flowering and marks many important changes in the vine. Prior to veraison, the vine invests its energy into growth and development. By veraison, the shoots are typically full height, and the vine’s energy is focused on fruit ripening. Color, flavor, and sugar begin accumulating in the fruit. Acidity and astringency decrease, and the fruit begins to soften. Berries continue increasing in size for several weeks after veraison, but cell enlargement, rather than cell division, is responsible for this increase.

Harvest & Post-Harvest

Depending on the desired level of ripeness, harvest ranges from 4 to 12 weeks after veraison for dry wine styles. Harvest for sweet wine styles may occur much later in the fall. Different varieties ripen at different rates, and ultimately, the winemaker decides when the fruit is ready to be harvested. Ripeness should be thought of as a spectrum, rather than a discrete point, and harvest timing within this ripening window has serious implications on wine style and expression of site.

After the fruit has been harvested, the canopy changes colors from green to yellow as leaves senesce. The vine redistributes energy from the canopy into the trunk and roots. During this time, the vine must store enough energy to provide for early development in the following year, from budbreak until leaves are big enough for photosynthesis. After nutrients have been translocated from leaves and shoots into the permanent features of the vine, the end of the season is marked by leaf fall, when spent leaves fall and the vine enters dormancy.