Winter and the Vineyard

A couple nights ago, Virginia vineyards were hit with a freeze. On Ox-Eye, temperatures dipped down to 23 degrees. If we had had bud-break, this could have been disastrous for the vintage. Many Virginia vineyards did have bud-break …

… some even had several inches of growth. Fortunately for us, our greenery is still tucked away in the swelling buds and seems to have been protected against damage. The vines aren’t dormant, though; the sap is running strong, and time will tell if there is trunk damage due to the freeze.

Every season my husband, John, the owner/grower/winemaker of Ox-Eye Vineyards, has something to worry about, and in the winter it’s about cold temperatures and moisture (or lack thereof.) I thought this would be a good time to interview John about winter issues in the vineyard. I started out with a simple question, the sort to which I already know the answer: “So, John. Tell me how snow effects the vines?”

“No real effect.” He stopped there, and I thought my interview was over. Then he continued, “Other than providing insulation against cold weather damage. And a slow leaching of moisture into the soil, which is good.”

So snow is good.

The cold issue is a little more complicated. My plan was to write this as a true interview, in Q/A style, but my fingers couldn’t type fast enough, so I had to paraphrase.

With a top elevation of 1,840 feet, Ox-Eye is a relatively cold-climate site. For that reason, John chooses cold climate varieties such as Riesling (our most cold hardy), Lemberger, Chardonnay, and Traminette. Generally, these vines can handle temperatures down to -10F, but the danger zone for temperature must be kept in context with how warm it’s been. If the winter has been sufficiently cold, then the vines should be dormant, making them less vulnerable to cold. A lengthy warm spell in, say, January, however, can present a problem if the temperature suddenly nosedives. That’s exactly what happened this year.

Why are freezing temperatures a problem? Vascular damage (that’s trunk splitting to us laymen). If a trunk splits, the vine will likely be lost. It’s possible to recover from vascular damage, but the vine is now weakened and susceptible to diseases such as crown gall, a form of plant cancer. When John sees crown gall, he knows the vine is suffering, but even crown gall isn’t always a death knell. If there’s healthy bud beneath the tumor, John will prune away the diseased portion and hope for the best.

The presence of spring greenery when the freeze (or frost) hits means probable loss of crop. If the grower is lucky, secondary growth will emerge, but the crop from secondary growth is significantly smaller than that from primary growth.

A fall freeze is also a danger because the vines might not have sufficiently hardened off. Hardening off is the gradual changing of new, green growth to woody vines. Vines begin this process in the fall, when they days are shorter, and continue all winter. If a vine hasn’t sufficiently hardened off before the first cold snap, part or all of the vine might die.

Is there anything a grower can do to protect vines/crop from an untimely freeze? Extreme measures (helicopters and windmills to stir air or push the warmer air below the colder air) are too expensive for most sites. Before bud-break, some growers might spray paraffinic oil to slow down bud-break by several days. After bud-break, some growers with overhead irrigation systems might spray water on the vines. The water will freeze over the greenery before the dangerously low temperatures hit, thus protecting the crop (hopefully). We don’t have this kind of irrigation system–in fact, we at Ox-Eye don’t irrigate at all.

John’s best advice to those considering entering the grape growing business is to choose a good site and to understand that site. A good site is sloped for air drainage, has relative elevation to avoid frost pockets, has deep and well draining soil, and has good aspect (in our case it’s East South East). Avoid western exposure because it encourages early bud-break, which could be disastrous (see above), or cause sunburnt fruit from the harsh afternoon sun.

Don’t buy into the latest fad grape. Look at long term empirical data for your area. Data for Virginia’s Piedmont is not the same as the Chesapeake, or the Shenandoah, etc. Check records for absolute highs and lows, heat/degree days, average dates of first and last frost, and compare this data with the requirements of the vine variety. Variety selection is key. There are a million blue grape varieties out there, and Virginia hasn’t scratched the surface between what may and may not work.