As Mike Andrews drove through south Central Washington, his sense of alarm grew with the darkness. He was returning from California, where he'd been looking at equipment, and the outside temperature plummeted as he neared his home and vineyard in the Horse Heaven Hills south of Prosser.
When he got there, he found the power out and the furnace not working. Pipes were frozen — and so were most of his grape buds. During this night — November 24th of last year — the temperature dropped 60 degrees, reaching -6 F around sunrise. Long-term damage was averted when the temperatures climbed back into double digits during the morning, so his vines will thrive in later years. Had the freeze lasted long enough to damage the trunks, even that would have been in doubt.
He estimates that 90 percent of his vineyard was severely affected, and that his 2011 crop will be 35 percent of normal. Other vineyards in the area have reported less damage. The freeze hit all of Eastern Washington, but the effects vary according to location and varietal. Cold air sinks, so areas at the bottom of slopes feel the brunt of such freezes. Cabernet sauvignon is fairly hardy, but merlot, syrah, grenache, and malbec are more vulnerable.
Freeze effects also depend on timing. Grapevines form buds for the next year's crop in the summer. Just a few months old and used to warm weather, these buds are especially prone to freeze injury in autumn. Vineyard managers can take samples of buds after a freeze to gauge the extent of the damage. This sampling determines how many buds to leave during winter pruning. On winter-damaged vines, leaving more than the normal number of buds can help make up for those lost.
Statewide, it's likely that less than 10 percent of production will be lost this year. Mature vines will return to normal next year. Vines planted in the last couple of years are more tender, and severely affected ones will need another year to reach maturity.
Consumers, though, care less about production, and more about quality.
Dr.Wade Wolfe, of Thurston Wolfe, having been in the Washington wine industry for 30 years, has seen plenty of freezes during this time. "We don't, in general, tend to produce the best red wines from crops that come from freeze-damaged vines," he allowed.
A grape bud is actually three buds in one. The largest is the primary bud, which is responsible for the vast majority of the fruit in a normal year. Being larger makes the primary bud more exposed and more likely to be damaged. In this case, the smaller secondary bud can act as a backup, but it starts a week or two later and produces less fruit. The tertiary bud backs up the first two, but produces only leaves.
Dr. Wolfe explained that after a winter freeze, a vineyard is often left with a mix of primary and secondary shoots. It's not always easy to tell them apart, and even if one could, the decision to expend the labor to prune these is hard to make for a grower already looking at a reduced crop. The mix results in uneven ripening. A grower can let the grapes hang longer at harvest to let the grapes born of secondary buds catch up, but this strategy has its own risks. Uneven ripening has obvious negative implications for quality.
Kevin Corliss suggests proper vineyard management can minimize this problem. Mr. Corliss, the vice president of vineyards for Chateau Ste. Michelle, also noted that spring frosts occurring after bud swell actually induce more variability in growth than winter freezes. Freezes complicate management of the vines, but "the quality of the crop can be excellent. In a lot of cases you're starting the beginning of the year with a pretty light crop," he said. This allows the root system of the vine, which hasn't been affected, to focus on a smaller number of grapes, resulting in good maturity. In a normal year, some fruit has to be sacrificed to achieve that.
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