Citrus growers didn't care much for it, but the recent cold snap has provided a welcome dose of "chill hours" for Kern County's nut, grape and cherry producers.

City folks can think of it as a sleep-like phenomenon: Fruit trees need a certain amount of time every year dormant in cold weather in order to bloom and produce properly. How much time they need, at what temperature, varies according to the type of fruit and the variety.

Until recently, some local growers were concerned about this season's chill-hour total. As of Christmas Eve, a weather station in the Arvin-Edison area had logged 224 hours below 45 degrees since Nov. 1. That was 52 percent below 2011's total on that date.

But by Thursday, thanks to more than a week's worth of cold temperatures in mid-January, the total had climbed to 635 chill hours -- just 19 percent shy of last year's level on the same date.

"We are catching up," said Craig Kallsen, a farm adviser with the University of California Cooperative Extension office in Bakersfield. "I mean, we needed these colder temperatures."

Central Valley citrus growers did not. In fact, they spent heavily this season -- $38 million in nine days, by one estimate -- on a variety of frost protection measures. These include wind mills and helicopters to bring warmer air down to ground level, and running water to bring down tree temperatures more directly.

It's hard to say how bad the damage was, but the trade association California Citrus Mutual estimates that the recent cold will end up ruining about 10 percent of the valley's remaining navel orange crop. For mandarins, which have a thinner skin and are more susceptible to the cold, this year's loss may total as much as 25 percent, according to the association.

That's a lot less than last year, when the mandarin crop suffered a 40 percent hit because of a freeze late in the season, association President Joel Nelsen said. Fortunately, there's a lot more acreage ready to produce this year, he added.

"I don't see any major market disruptions as far as the consumer is concerned," Nelsen said.

The outlook is much better for Kern County's stone fruit, pistachio, almond and table grape growers -- but the risk isn't over yet.

Don Davis, an almond grower in the McFarland-Delano, said his team continues to monitor temperatures. The main concern now, he said, is that the weather could turn warm and then cold again.

"Right now the low temperatures are slowing down the bloom, slowing down the (crop's) development," he said, adding that a freeze before mid-April could still destroy almond blossoms.

But lately the weather has made him optimistic.

"I think the chilling hours have been enough. We're set," he said. "We're ready for things to start warming up in February. As long as we don't go back to frost in March."

Mark Hall, a grape farmer in the Wheeler Ridge area, said he's feeling confident about the amount of chill hours this year's crop has received.

He said most of his vines required no special protection, although he did use a chemical treatment on one seedless variety known as Sugraone to regulate the vines' growth during low temperatures.

"Grapes are doing fine," he said. "This cold weather doesn't hurt them ... in fact, it helps them."

Local farmers and agriculture officials say it's routine to pay constant attention to temperatures and take preventative measures. It's why the Kern County Farm Bureau is working on a new system to issue weather alerts to its members, said the group's executive director, Ben McFarland.

"It's just part of growing that crop," he said.

Not until the orchards start blooming will growers know whether their vigilance has paid off, said Kallsen of the Cooperative Extension office.

"We won't know really what happens," he said, "until the spring."