Fanning the frost away

We’ve had some gorgeous spring afternoons here in Carneros this past week but we’ve also had some damn cold mornings.

Those cold morning temperatures bring the danger of frost, which can kill the tender, green shoots that have sprouted on the vines. To prevent the frost from settling on the vines a common method here in Carneros is to crank up the huge wind machines. The machines look like an airplane engine that’s been mounted on a pylon about 20 feet tall. And when all the props start turning at around 4 a.m., it sounds like a squadron of fighter planes idling on the deck of a World War II aircraft carrier.

The first frost warning of the season came about two weeks ago. I remember I walked out of the house at around 5:15 a.m. to go for a run and could hear a loud whirring, humming noise that sounded like a helicopter. In my drowsy state, I thought a helicopter was hovering nearby and I leaped to the conclusion that a grower had hired a chopper to hover over his vines to protect them from frost. (Well, at first I thought the cops had raided a meth lab and had a police helicopter hovering overhead with a spotlight, but that was just too ludicrous.) After starting on my run, I soon discovered it was just a simple wind machine.

Frost caused significant damage in the months leading up to 2009’s harvest, but I haven’t heard of any major frost problems so far. With temperatures dipping into the mid-30s, however, growers have to be careful.

My father in law, who spent his entire career in viticulture and was educated in France, noted on Saturday that a few growers have made the mistake of tilling the rows between their vines. Uprooting the cover crop between vine rows can expose the soil, and the vine, to frost. Tilling the ground robs the ground of its natural insulator.

Another way to protect against frost is to  freeze the vines. A vineyard manager friend of mine told me his company cultivates vines in Pope Valley in the northern corner of Napa County. He said there are a few vineyards up there at higher elevation that can be subject to quick and damaging temperature changes. When a forecast calls for temps that will drop far below freezing, he said they’ll turn on the sprinklers to freeze the vines. This method will encase the vines in ice and keep them at a constant temperature that will stay higher relative to the air temperature, which can keep dropping into the low ’20s. He said it’s a surreal sight to arrive at the vineyard and see the plants locked in ice.

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