Warm weather hastens bud break in vineyards
Mid-April might be spring to most residents of the Grand Valley but grape growers know better.
“Traditionally our last frost here is April 23, but that’s never a given,” said Nancy Janes of Whitewater Hill Vineyards on 32 Road.
In what may be a sign of climate change, that last frost is coming earlier, said state viticulturist Horst Caspari of the Colorado State University Orchard Mesa Research Station.
“Our last spring frost has moved forward (earlier) by about a week,” said Caspari, citing records going back to 1964. “And our first killing frost is about one week later.”
That’s only an average. In 2010, the last killing frost came on May 7, Caspari said.
“But we had such a late bud break there was very little damage,” he said. “Of course, we had so few buds (surviving from the December 2009 cold snap) it didn’t matter.”
On a recent cool and breezy April afternoon, Janes and a visitor walked the edges of a 6.5-acre vineyard near her winery on 32 Road.
Like many vineyards in the valley, it wasn’t pruned last year but simply left to produce leaves and let the plant heal. This spring finds those vines wildly tousled, every vine sprouting a Medusa-like growth of one-and two-year old stalks or canes.
It’s quite unlike something you might see in a normal spring when pruning would have been finished by now but Janes and her husband John Behr opted for waiting to see what her cold-damaged plants would produce.
In December 2009, Janes saw minus 17 at a vineyards on 34 Road and minus 10 at her winery.
“We lost everything to the ground” on 34 Road, she said.
That vineyard, like others where the frost killed the vine trunks to the ground, was chopped down and left to sprout new growth.
Because Grand Valley grapes largely are own-rooted, unlike other states where grape vines are grafted onto to disease-resistant roots, Grand Valley growers enjoy the relative luxury of knowing what they’ll find sprouting from the old trunk.
In Janes' case, the merlot, shiraz and other varietals she lost in 2009 have shot up bright new canes, the light tan wood and many buds promising clusters of grapes later this summer.
“We want to keep these smooth, light-tan canes because the grapes are all on last year’s wood,” said Janes, welding her knife-edged pruners on a grayish length of shiraz vine. “But this, the striated wood, is second-year growth and will be cut off.”
And snip, it was done.
“We’ll come through here later and prune it back in ‘traditional’ style,” said Janes, looking down the long rows of vines and silenty counting the long hours of work ahead.
For her, traditional means means leaving a cane spur (or branch) every hand width (about 4 inches) along the cordon or main vine, with two buds on every spur. Each bud produces two clusters of grapes.
Most of the valley’s grape buds have reached the “wool” stage, said Caspari, and if you look at each pencil eraser-sized bud you’ll see a furry growth at the sprouting end. It’s a sign that bud break, when something green starts to sprout, is not far off.
“From the fuzzy wool stage to first green growth is seven to 10 days at a constant 70-degree temperature,” he said. “Nothing will move at 50 degrees but the more over 50 we are the faster it grows."
Pruning can start as early as mid-February and a drive through East Orchard Mesa shows many vineyards already neatly cut back, ready for the summer growing season.
Janes and Behr sometimes delay their final pruning until bud break, when they know which buds are going to produce.
“We’ll come back to do our fine-tuning but it can be a real challenge to get it done” because the vines already have started sending out new growth, she said, gazing across the acres of tangled vines.
Casapari has been out spending long days in the vineyards near the Orchard Mesa Research Station.
"With the mess of new shoots and deciding what to keep and what to throw out, the pruning takes extremely long this year,” Caspari said. “We are spending 150 hours pruning one acre and we should be doing it in 30.”