While we spent last month shivering and complaining about the polar vortex, local vintners were nervously checking their thermometers as record low temperatures threatened to damage their vines.

Grapevines are dormant this season, but they are not immune to the vagaries of winter. Sustained low temperatures can damage the buds that eventually will carry this year’s crop, and sudden, severe temperature drops can even kill the vines. Vintners won’t know the winter’s true effects until the growing season starts in spring, but there have been reports of extensive damage to vineyards in Ohio and Michigan. Cornell University reported bud damage in New York’s Finger Lakes, especially to Riesling and merlot vines around the northern end of Seneca Lake.

“When temperatures get to the single digits, grape growers tend to get concerned,” says Doug Fabbioli, owner and winegrower at Fabbioli Cellars in Virginia’s Loudoun County. “Each varietal has its winter damage temperature. On the higher number would be merlot at 0 degrees, meaning that it’s more sensitive than cabernet franc at minus 10.” The windchill factor magnifies winter’s effects on humans but not on vines.

Healthy vines are a vineyard’s best defense, Fabbioli said. Vines contain stored energy in the form of sugars from photosynthesis during the past year’s growing season, and the sugars act as a sort of antifreeze during harsh winters.

“Many growers have not surveyed their buds yet. I think they’re scared,” Mark Chien, viticulture educator for Penn State Extension, said in a Jan. 28 e-mail. Chien said he’d conducted a pruning workshop the day before at Waltz Vineyards in Lancaster County and found the vines in good shape: “We had good acclimation conditions in the fall, and I think that has led to very cold-hardy vines.”

So if the worst we can expect locally is bud damage, what does that mean for the 2014 growing season? A smaller crop, potentially, but even that effect can be moderated with care in the vineyard. “You’re going to cut most buds away during pruning anyway,” Joseph Fiola, viticulturist at the University of Maryland, explained to me in early January. So if some buds are damaged, the grower can prune accordingly to give the vine more chances to produce fruit. “As long as you haven’t pruned too early, you’re fine,” Fiola said.

Most growers begin pruning in late January or February, though some have moved pruning earlier after several mild winters reduced the concern over winter damage, according to Tony Wolf, Virginia Tech’s viticulturist.

Wolf cites a “silver lining” for regional vintners in this year’s harsh weather. Pierce’s disease, a vine-killing virus carried into vineyards by insects called sharpshooters, thrives on warm winter conditions and had been creeping north into Virginia’s vineyards. “Cold winter temperatures are beneficial in keeping this particular disease further to our south,” he said via e-mail.

California vintners are dealing with the opposite problem, and with potentially serious effects. With temperatures in northern California unseasonably warm, early-budding grape varieties such as chardonnay are showing signs of growth already — a month earlier than normal — while the region deals with record drought.

Last year was the driest ever measured for Napa Valley, with just four to eight inches of rain, according to the Napa Valley Grapegrowers. The area typically gets 12 to 25 inches of rain annually, with eight inches on average falling in January. This past January was dry.

Winery ponds that collect rainwater to use in irrigating vineyards during the summer are drying up, so growers are already planning for lower crop yields. If you visit California wine country this year, you might notice less-abundant foliage on the vines and a lack of cover crops between the vine rows. Those cover crops provide nutrients to the soils and guard against erosion, but they compete with the vines for water.

The ponds are also used for frost protection: Spraying the vines during a frost protects the fragile flowers from the cold. With the season starting early, the vines will be at greater risk for frost damage.

As with conditions here in the East, it’s too early to gauge what effect this unusual winter will have on the 2014 California harvest. But the concerns demonstrate that even in the dormant season, vineyards are susceptible to nature’s whims.

McIntyre blogs at dmwineline.com. On Twitter: @dmwine.

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