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Early spring? Not for grapes, who like it warm

By Dave Buchanan

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. "Our average (daily) high is running about 5.5 degrees warmer than average,” said Horst Caspari, state viticulturist at the Orchard Mesa Research Station.

It’s not yet a big or long-term trend, since Caspari noted the previous year was cooler than average. But even with the warmer temperatures, it still hasn’t been warm enough long enough to cause grape vines 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. Those two weeks turned into one week, culminating in Sunday's storm and by Tuesday temperatures again were edging back in the 40s.

According to Caspari, 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. Meaning a plant will respond greater to a warm March spell than what pass for warm days in Janauary, when warm might mean touching 45 for an hour or two and then plunging back to single digits at night.

Now, with February entering its final week, spring or it’s 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.

How ever solid good your math, grape growers have an added advantage over the orchardists since late-breaking grape buds aren’t as susceptible to early spring frosts. Late frosts, though, 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 expect to get little sleep until well into May.

Climate trends are all the news and there is one being followed in the North Fork Valley. Caspari said grape growers there 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 years 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, but it was late in the sense the grapes were just barely ripe enough,” said the founder and winemaker for Alfred Eames Cellars. “But they shut down and I couldn't wait.”

Grape growers closer to the valley floor didn't see the same cold as Peterson and he said it was because a breeze kept the cold air moving. 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.

"The fact the wind was blowing down there in the canyon saved them," he said. "That sometimes happens here. If it hadn't be blowing down there, it would have frozen them more than us." Peterson said grapes were in short supply to the point where this year he won't be making an estate reserve pinot noir.

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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