With the return of interest in wines of freshness, energy, and more delicate presentation, interest in cool climate wines has also increased. Without a formal definition, the idea of cool climate gets applied generously to regions around the world. Climate classification systems based on growing degree days and mean temperature indexes provide only limited insight into the actual growing conditions of a region. Many regions commonly referred to as cool climate host daytime temperatures reaching highs comparable to recognized warmer climates, allowing plenty of ripeness for the right varieties.
Genuinely cool climates, however, tend to successfully grow only varieties that ripen earlier, before temperatures drop. Temperatures at harvest are often quite a bit cooler than those during the peak of the growing season, slowing metabolic processes in the vine. The temperature of the fruit itself at harvest is usually lower as well.
As winegrowing has extended into more regions around the globe, it has also pushed further into the edges of possible winegrowing. Such expansion has changed our views of viticulture. We’ve realized we can grow in more extreme conditions than previously believed. At the same time, these changes have required us to develop our understanding of how to more successfully grow in truly marginal climates.
But what are the conditions of a marginal climate?
Marginal climates are the coldest growing regions in the world, with weather conditions that tend to vary significantly by vintage, and, as a result, present the real possibility of failing to adequately ripen fruit in some years. Such conditions tend to be found in higher elevations, as well as higher latitudes, where nighttime temperatures often have a significant drop, there is a more marked variation between seasons, and light conditions differ. More varied diurnal shift and seasonal temperatures are common in these climates as well. Though maritime climates can also suffer difficult issues such as frost or freeze, proximity to large bodies of water provides a moderating influence.
Though we tend to think of cool climate conditions as growing more delicate, energetic, and mouthwatering wines compared to the richer flavored, bigger volume wines of a warmer climate, conditions in a marginal climate can actually mix up that dichotomy. Marginal climates tend to include significant weather variation from year to year, leading to marked vintage variation in the resulting wines.
Converse to expectations, marginal climates can create bigger or heavier wines. Extended growing seasons, the result of a cooler vintage, can lead to reduced acidity, as the increased length of the season leads to more respiration of the vine. Since respiration naturally reduces malic acid levels, longer growing seasons change the natural acidity of the wine. It is not as simple, though, as the length of the growing season alone. Colder regions also tend to have wind, which has a significant impact on the vine. Wind speeds of eight miles per hour and higher cause the stomata of the vine leaf to close, slowing respiration and thus preserving higher levels of natural acidity. Even so, vintages with much lower malic acid levels will have a noticeably different shape on the palate as compared to those with higher malic acid levels, whether or not the final wines go through malolactic conversion.
Cooler temperatures and wind exposure generally lead to grapes with thicker skins, thereby changing the skin-to-juice ratio of the fruit. Grapes with thicker skins tend to produce more concentrated wines even without excess purposeful extraction in the cellar. The thicker skins can offer further benefit: since skin tannin is more pleasant and less bitter than seed tannin, thicker skins can create better balance in the final wine. Thicker skins help produce a structured wine with the potential to age without relying as heavily on harsher seed tannin. As a result, wines from such conditions often have the double benefit of the structure to age alongside approachability in their youth.
The timing of weather conditions during the growing season also importantly impacts the size of the final wine. Wind, rain, and snow are more common early in the season in colder climates. In years in which such conditions hit during flowering, bloom, or fruit set, yields are reduced. Because vines with lower yields effectively have less work to ripen their crop, fruit in such conditions tends to ripen more quickly, making it easier to end up with higher alcohol wines in low-yield years—even in cooler climates.
Growing conditions of a marginal climate include, too, the question of fog. The flavor and structural balance of a final wine depend not only on the temperature of a region but also on the naturally occurring light levels. Cooler climates can still have ample sun exposure in regions with little fog. Temperature tends to impact the duration of the growing season, and thus also the respiration of acidity, leading to changes in the style of the final wine. Sun exposure, on the other hand, influences the sugar development of the final wine, thus changing the potential alcohol. Both lead to evolution of flavor. As a result, in the right conditions, a genuinely cool vintage can still readily produce a high alcohol wine, especially in a year where thicker skins need more time to soften or seeds need more time to develop.
To grow wine in a marginal climate, it’s key to select the right grape varieties, identify a proper site and carefully construct its architecture, and protect against freeze.
In honing viticulture for a marginal climate, the most important step is selecting the right grape varieties. Generally, in cooler climates, earlier ripening varieties are preferred. Müller-Thurgau, Chasselas, Gewurztraminer, Gamay, and Pinot Noir are all examples. Chardonnay is also an early-ripening variety, but because it has early bud break, it can be difficult to grow reliably in climates that experience spring frost. Riesling can succeed in a cooler climate if planted in a location that receives warmer temperatures during the growing season to help elevate ripening.
While we tend to talk about cool climate characteristics in varieties such as Syrah, Cabernet Franc, and Merlot, they do not succeed in regions with a genuinely short growing season or the threat of winter freeze. As they are later-ripening varieties, they can be grown in climates that have cooler temperatures but not those with the threat of snow or freeze in autumn.
In climates with the threat of extreme winter conditions, choosing varieties that are winter-hardy is essential. Doing so can be tricky in more marginal climates, as many varieties that ripen in cooler temperatures are also more susceptible to freeze. The most winter-hardy varieties tend to be American grapes, followed by hybrids, and then finally European varieties. Some European varieties are more winter-hardy than others. Varieties such as Cabernet Franc and Riesling are more winter-hardy than Pinot Noir or Chardonnay, but they also need warmer temperatures during the growing season. Selecting winter-hardy rootstock can help as well.
Once varieties appropriate to the climate are identified, selection of the right site is crucial.
In spring, cold weather events can cause frost damage on the surface of the vine. Because this usually occurs at the same time vines are experiencing bud break, such damage can be devastating, destroying an entire year’s crop. Freeze, on the other hand, typically occurs late in the fall, a tremendous threat for late-ripening varieties. Frost and freeze are problems not only because they can cause the loss of a year’s crop but also because surface damage to the vine can make it vulnerable to a bacterial infection called crown gall. At its worse, crown gall can kill the entire vine. In climates with winter conditions during the longest nights of the year, vines must further be protected from complete freeze of the vine itself, not just its surface. Temperatures cold enough to cause freeze inside the vine will kill its trunk.
The best protection against frost or freeze is selecting a site less vulnerable to it. In climates that can experience frost, no site is truly immune, but sites can be found that are essentially invulnerable to more common frost events.
There are two types of frost events. Most common is radiation, or ground frost, which occurs when the ground reaches a temperature lower than the air above it. This is the type of frost that results in white frost blanketing the ground in the morning. Some ground frost is acceptable for vines, as in the right conditions it will perform what is essentially a natural pruning process, causing lower buds to drop. But if ground frost continues for too long, the cooler temperatures lift higher into the air, lowering temperatures surrounding the upper parts of the vine as well. This is when frost protection measures such as wind machines, helicopters, or overhead sprinklers must be used. In such conditions, wind machines or helicopters work by circulating the air around the vineyard, thus pushing the warmer air above the vineyard down toward the ground. It is, however, possible to find sites that are unlikely to ever suffer from this sort of frost.
The second type of frost is advection frost. This occurs when a huge mass of cold air from a large weather system moves into a region during a storm. The cold air mass is so large that it settles over an entire region, and no site remains unaffected. The frost that settled into much of France this spring and the frost that damaged regions throughout Chile in 2013 are two examples of advection frost. It is difficult to protect against damage with this type of frost. Wind machines or helicopters have no benefit, as the air is not only cold close to the ground but in the air above the vineyard, so there is no warm air to be circulated. Heat burners can sometimes help, though it is difficult to get enough lit quickly. If the storm does not last for too many days in a row, water protection can help.
In selecting a site that is less vulnerable to ground frost, the topography of the landscape is most important. Proximity to water can be beneficial, too. Cold air essentially flows like water, reliably moving downhill and around obstacles. As a result, sites higher up on a slope or at the edge of a natural drop like the edge of a canyon tend to be less likely to suffer frost events. Obstacles in the landscape, like a tree barrier partway up a hill, can change that, as the cold air moving downhill will naturally pool before the obstacle. Low spots in a landscape, such as the bottom of a hill or even a low dip in an otherwise apparently flat landscape, tend to be more frost prone.
Larger bodies of water can help protect against both frost and freeze events. For example, in the Niagara Escarpment of Ontario, vineyards can only be successfully grown within visual distance of the lake. Those outside a couple miles of the water are too cold in winter for vines to survive.
When frost damage does occur, it is now understood that vines should be allowed a period to recover on their own. Until recently, it was believed that if buds or leaves were damaged by frost, they should be immediately removed. Yet contemporary viticulture has found that it is beneficial to leave frost damage alone. From milder damage, the vine can recover on its own. Even when a bud is properly damaged by frost, it is possible for a vine to push a replacement bud in the same spot if the damage occurs early enough in the season. Swift removal of a damaged bud, however, seems to cause further damage, preventing the vine from forming the replacement bud.
Once a site is selected for a hardy vineyard, the goal is to design the vineyard architecture to reduce overall vine stress. A vine’s carbohydrate levels protect it against colder temperatures, reducing potential damage. Limiting vine stress helps preserve the energy the vine needs to produce adequate carbohydrate levels for this protection. It is essential to keep crop levels moderate. Matching training methods to the conditions of the site and the needs of the variety are also important, as is timing winter pruning to allow the vine ample dormancy.
Once vines are planted, the treatment of the rest of the vineyard directly surrounding the vines is relevant. While cover crops can be beneficial during the winter, in spring, when frost season begins, it is best to remove all or most growth at ground level below the vines. Because frost depends on airflow, removing growth below the vines removes obstructions, allowing the air to more readily move through the vineyard rather than pooling within it.
The height at which vines should be trained depends on other growing conditions of the area. In many cases, training the vines further from the ground ensures they will be less vulnerable to the cold air collecting near the ground. In areas with ample dark rocks in the vineyard, such as The Rocks District of Milton-Freewater in Walla Walla, or Châteauneuf-du-Pape in the Rhône, training lower to the ground can be of benefit, as the dark rocks absorb heat from the sun during the day, which is then radiated to the vines at night.
Continental climates tend to have cold winter temperatures that can sit below freezing for extended periods of time. In such conditions, vines are vulnerable to freeze damage that can cause full trunk loss. In these environments, growers have developed more involved ways to protect vineyards.
Though Walla Walla is by no means a marginal climate, it does experience extreme freeze events in the winter. As a result, the area has suffered severe vine loss several times in the last decade. Growers bury a reserve cane underground during the winter months to act as insurance against the possibility of freeze. During the growing season, an extra cane low on the vine is allowed to develop. It is not used to produce fruit but is kept in reserve to be buried under topsoil at the end of the season. If no freeze occurs, the reserve cane is pruned in spring, and a new reserve cane is started. If, however, there is vine damage from severe freeze, the damaged trunk is cut away, and the reserve cane is lifted and trained as the new vine trunk. In this way, a season is not lost even with trunk damage.
In even more extreme winter conditions, such as parts of Canada, entire vineyards are buried. Here, growers will place a covering sheet over a row of vines and then cover the sheet with topsoil for the winter. Snow falls on the buried vineyard, providing additional insulation. In the spring after snowmelt, the topsoil and covering is removed, and vines are pruned as normal.
Growing in marginal climates certainly presents significant challenges. But with proper site selection and vineyard maintenance, the resulting wines can offer innate flavor concentration with the right structure for long aging, while still being approachable soon after release.