Wine Openers

State viticulturist Horst Caspari points to where cold air pools and kills grape vines in an vineyard on East Orchard Mesa near Palisade, Colo.

EAST ORCHARD MESA – The thump of wind machines waking you last week wasn’t a dream but an attempt by grape growers to ward off the vine-killing cold.

However, it’s been grape-deathly cold in some spots for several weeks and grape growers tardy in cranking up the 30-foot high wind turbines may be too late to prevent losing part or all of next year’s crop, warned state viticulturist Horst Caspari at the Western Colorado Research Center on East Orchard Mesa.

“We have a maximum on cold-hardiness our grapes can reach and if we get below that, it’s done,” he said. “But if you have a wind machine to use and you don’t use it under the conditions we have now, we haven’t learned anything from 2009.”

That was the winter when a December deep freeze sent the temperature in western parts of the valley plunging to 22 below zero and more than 50 percent of the vines in the valley suffered extensive damage, with many growers losing most of their 2010 crop.

Temperatures this year have flirted with that low mark – a minus 18 was registered recently near Fruita – but along with temperature growers also must consider wind speed and length of exposure to the cold, Caspari said.

A few minutes at 28 degrees won’t bother most grape buds but longer exposures at the temperature can kill them as surely as 18-below.

As grapes and other fruit go dormant, their cold-resistance increases. But once the plants reach their most-dormant, temperatures below that may kill or damage the bud or vines.

Wind machines mix warmer air from 100 feet or more with frigid ground-level air trapped by inversions or pooling behind physical dams such as building or trees.

Fans may only bring a rise of 3 or 4 degrees, but that can be sufficient to save a crop.

The easternmost part of the valley benefits from a year-round breeze from DeBeque Canyon. The breeze acts as a natural wind machine, keeping that part of the valley warmer by not allowing the cold air to pool.

The cold air certainly gathers along the Colorado River, where pockets of air can be minus 8 or 10 when it’s minus 1 on East Orchard Mesa, where the cold air flows off the north-sloping fields and lands along the river.

“We didn’t run our machines (Sunday) night but we did the three previous nights,” said Galen Wallace, vineyard manager for Plum Creek Cellars’ vines on East Orchard Mesa, well above the coldest layers of air.

Still, there are enough microclimates in the gullies and ravines that monitoring the temperature is “huge in this business,” Wallace said. “We get 10 percent (bud) damage at 5-below so I watch it closely and when it gets to 1-below I’m ready” to start the wind machines.

Surprisingly, the valley’s largest grape grower hasn’t yet run his wind machines.

“No, we haven’t run our machines yet and that’s probably a mistake,” said Bruce Talbot, who farms 150 acres of grapes and 300 acres of peaches across Orchard Mesa and East Orchard Mesa.

“The peaches are just fine but we know the grapes are sensitive right now,” Talbott said. “We were told the grapes can take 10 below and if we get close to that we can sustain damage, so we try to minimize that.

“But so far, minus 2 and minus 4 are what we’ve seen in town.”

Caspari said that temperature might be misleading, since it probably measures temperate at cordon height (about 40 inches) and not at ground level, which could be several degrees colder.

“So it’s four degrees colder at snow level and where some of his vines are might be 5 degrees colder than the weather site, so that’s minus 4 and another 5, that’s 9 degrees, so it’s really 13 below right above the snow line,” Caspari estimated. “Bye, bye, it’s toast.”

More on cold and grapes next week.