Sonoma County grape growers battling to protect vineyards from frost

With overnight temperatures dropping toward freezing and beyond several days this week, it’s been a stressful time for vineyard operators in areas of Sonoma County, with many out in the dark trying to save their crops on back-to-back nights.

An especially early bud break put cool-climate chardonnay and pinot noir vines in jeopardy in low-lying areas from Petaluma to Cloverdale, and weather forecasts suggested a third consecutive night of frost protection efforts lay in wait Thursday for those in charge of seeing this year’s grapes through to harvest.

“We get frost this time every year, so we’re usually prepared for it,” said Jeff Carlton, president of the Sonoma County Farm Bureau and vineyard manager at Dutton Ranch. “Last year was kind of an anomaly. We had zero times last spring. You’ve just got to be vigilant this time of year, make sure you don’t have any frost damage.”

The temperature bottomed out at 30 degrees overnight Wednesday into Thursday at the Charles M. Schulz-Sonoma County Airport, according to meteorologist Roger Gass at the National Weather Service.

This was already a record low for March 26. But unofficial sites reported temperatures of 28 and 29 degrees, he and several grape growers said.

The tender leaves that erupt in early spring, when overnight temperatures still range widely, are followed by flower clusters. If damaged by frost, they can limit a vineyard’s fruit production, though affected vines will try to push out second and even third buds, Carlton said.

But most vineyards in locations subject to frost are equipped with automatically triggered fans designed to mix upper layers of warmer air with the coldest air near the earth’s surface. Some also are equipped with sprinklers that encase the buds in frozen water to keep them at a constant 32 degrees.

Vineyard owners, managers and their crews still need to be out and about checking equipment in the event something goes awry, as it did in at least one area at Dutton Ranch early Thursday, Carlton said.

“One hard freeze could wipe out half your crop,” he said. “There were a lot of guys running frost protection early this morning. A lot of guys.”

The National Weather Service had another frost advisory in effect for early Friday morning, with temperatures expected around the same levels as early Thursday, Gass said.

Most growers and their crews spent Thursday afternoon getting some rest in preparation for another long night.

“Like now, we’ve got a lot of clouds hanging around out there,” Sebastopol grower Domenic Carinalli said Thursday. “That all helps.

“We just gotta see how it plays out. It’s that time of year.”

You can reach Staff Writer Mary Callahan at 707-521-5249 or mary.callahan@pressdemocrat.com. On Twitter @MaryCallahanB.