Wine Openers: Cold temps welcomed by grape growers

Warmer temperatures in January and early February weren’t enough to spur bud break on local grape vines.  An early bud break would leave vines more susceptible to spring frost damage.

Sunday’s snowstorm and cold temperatures may have come as a shock to those already thinking spring had arrived in the Grand Valley, but it was a good thing for the area’s grape crop.

While the moisture was needed, it’s the return to cold temperatures that’s really welcome.

That the winter has been warmer than usual doesn’t surprise many people, but the degree to which it’s been warmer might.

“Compared to last year, our average high is running about 5 1/2 degrees above average,” said Horst Caspari, state viticulturist at the Orchard Mesa Research Station.

It’s not a big trend, since the previous year was cooler than average, said Caspari in late January.

But even with the warmer temperatures, it still hasn’t been warm enough to cause grapevines to break dormancy and start sending out new shoots.

“We’ve seen this before and if we get two to three cold weeks in February everything will slip back,” he said.

The magic temperature (magic in the way that plants start to respond) is 50 degrees, but it takes more than simply reaching 50 degrees to begin the processes of spring.

Plants (and it differs with nearly every plant) need a certain number of growing degree days, when the 24-hour temperature average is 50 or above, to start their growth cycle.

Hitting 50 or 58, as it did briefly earlier this winter, isn’t enough to signal it’s spring, because the temperature still was dropping well below that threshold every evening.

And even receiving two weeks of warm weather in January and February, with winter still ready to come roaring back, aren’t enough to break that winter’s sleep.

“A really warm day in March makes up for 15 warm days in January,” Caspari said.

Now, with February entering its final full week, spring or its thermographic equivalent might really be around the corner.

“We don’t get real heat degree days until late February,” Caspari said, which means you can expect to see some action any day now.

If you’re really curious, you can figure growing degree days by taking the day’s high temperature, adding the low temperature and divide the result by two.

Subtract the base temperature (50) and you get degree days.

Grape growers have an advantage over the orchardists because late-breaking grape buds aren’t as susceptible to early spring frosts.

Late frosts, such as the one last May that damaged vines across the valley, are a distinct danger, which is why grape growers have invested in wind machines and frost alarms.

Climate trends are all the news and there is one being followed in the North Fork Valley.

Caspari said grape growers who a decade ago were growing pinot noir with ease now are struggling to get that notoriously fickle grape to mature.

“There’s been a few year when they’ve had extremely cold winters, early freezes and later springs,” Caspari said. “They started out with a few good years from 1996 to 2000 but pinot noir doesn’t grow well right now.”

During a conversation with Paonia winemaker Eames Peterson, who delights in making excellent pinot noirs, he mentioned the 2011 harvest was a bit rough.

“It got cold and froze and I was forced to harvest in October, which for me is not really late,” he said. “But they shut down, I couldn’t wait.”

Freezing causes grape vines to stop growing, cutting off the stream of nutrients to leaves and fruit, and grapes start to dehydrate on the vine.

Peterson said his last big harvest was 2009, when he made 1,700 cases of wine. He ranks that vintage as the best he’s made.

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