Winter

Unlike the lush growth spurred by summer, winter pares a vineyard down to its bones. Vines drop their leaves, revealing spindly arms and crusted trunks. To the untrained eye, it might look bleak. Yet, important processes take place, like bud and root growth, pruning, suppression of pests, disease and more. The writer Paul Theroux once said that “winter is a season of recovery and preparation.” It captures the mindset of vignerons during the cold, dark days that cause many of us to grumble. After the fall harvest, vines may mature and harden their renewal buds for the next growing season. Then, their root systems may expand to suck up nutrients in a “late-season growth spurt,” says Dan Sullivan, winemaker and co-founder of Rosehall Run Vineyards in Prince Edward County, Canada. Dormancy comes next. It’s the state that perennial plants like grapevines enter at the end of their annual cycle. As temperatures drop and days shorten, active vegetative growth dwindles. Vines move through deepening stages of rest. Ecodormancy, triggered by autumn’s gradual tilt away from the sun, phases into endodormancy, the vine’s version of REM sleep. Just as people loathe jumping straight from shorts to puffer jackets, for vines, “acclimating to winter is best if it happens gradually,” says Sullivan. This period of rest is vital to recovery. The vine’s slower metabolism allows it to stockpile carbohydrates for when vines transition, or deacclimate, into spring. Think of it as grizzly bear hibernation for Pinot Noir and Riesling vines. Due to climate change, weather patterns shift and create new challenges. There’s been much discussion about summer heat and drought, but winters have changed, too. Dormancy length and temperature variation depend on a region’s geographical latitude. Most Vitis vinifera, or common grapevines, grow where seasonal transitions occur in both hemispheres. While vines have some cold weather resilience, generally to -5°F, vineyards in northerly regions like Canada and Hokkaido, Japan, face increased challenges, particularly from polar vortex storms. Rapid temperature drops and deep freezes test the resolve of both vines and vintners, says Sullivan. He buries his budwood for the following season with soil. “This provides adequate insulation to protect the vines to temperatures below 20°F,” he says. “Snow is also a good insulator.” Wild weather swings pose hazards for endodormant vines, too, says Moritz Haidle, winemaker at organic family winery Weingut Karl Haidle in Württemberg, Germany. “If it turns warm in the middle of winter and the vine thinks that spring is starting and gets juice in its veins, [and] then it gets cold again, that’s dangerous,” he says. Once vines go full Sleeping Beauty, farmers head into fields to prune. Haidle waits until the last leaf is gone, often in early January, to trim back the prior year’s growth. Pruning supports vineyard health, defines future yields and shapes vines for growth and training structures like the “gobelet” bush vines of Priorat, versus the vertical shoot positioning common in California. Bare branches make pruning easier, too. “The most important consideration in winter pruning is to prevent the spread of vine trunk diseases,” says Brandon Sparks-Gillis, co-owner and covigneron of Dragonette Cellars in Santa Barbara, California. Like many growers, Dragonette must combat destructive maladies like Eutypa dieback, a fungal infection that progressively kills the plant. Symptomatic or dead vines are spotted more easily in winter. However, farmers must take extra care if they prune on windy and rainy days, when spores can disperse into fresh cuts. Spring brings its own challenges to pruning. “In Santa Barbara County, two of our main viticultural risks are late-spring frost and shatter due to high-wind velocity at bloom time,” says Sparks-Gillis. His team mitigates these perils by pruning late in winter. This delays bud break, the first green growth to appear on a waking vine when temperatures warm. Frost damages tender buds and young leaves, which can reduce a farmer’s crop. If bud break occurs later, harvest gets pushed past “peak summer temperatures,” says Sparks-Gillis, so they can pick fruit in cooler, more favorable conditions. Winter’s colder temperatures also help suppress pest populations. Sparks-Gillis points to the historic drought between 2012 and 2017 as evidence. “During the…drought, the mild winters in California were problematic because they failed to knock back the glassy-winged sharpshooter populations,” he says. “As a result, their populations grew and Pierce’s disease surged, causing widespread damage, particularly in the Sta. Rita Hills [American Viticultural Area].” Other winter benefits are specific to regions. California welcomes its annual soil saturation between November and March. Rains replenish aquifers and reservoirs, but they also cleanse the soil, says Sparks-Gillis. “Winter rains are important in our region because they help prevent salt buildup in soils which is toxic to vines…a problem during drought years,” he says. “If we receive multiple storms…the soils are cleansed and the next growing season has less hydric stress.” Haidle says that winter precipitation has taken on greater importance in hydrating Germany’s vineyards, too. Snowmelt and rain now compensate for Germany’s drier summers. Due to climate change, weather patterns shift and create new challenges. There’s been much discussion about summer heat and drought, but winters have changed, too. The implications of subsiding winters worry growers worldwide. “Dormancy is getting shorter because of mild winters,” says Haidle. “That’s partly why harvest was so early in the past few years. This also increases the threat of late frosts.” Sparks-Gillis has noticed more variability during winter and the whole growing season, with a trend toward warmer, drier conditions. “This is troubling due to the issues of salt toxicity and the spread of Pierce’s disease,” he says. And so, if we love wine, we must learn to love winter.