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  • Staff photo by Bob Hammerstrom

    Rick Hardy from Brookdale Farms in Hollis looks over peach tree blossoms that were frozen overnight Tuesday, March 27, 2012. He said they lost about 10 percent of the apple tree blossoms and around three percent of the peach blossoms to frost.
  • Staff photo by Bob Hammerstrom

    These peach blossoms will die from the frostaccording to Rick Hardy at Brookdale Fruit Farm in Hollis. Blossoms that haven't opened are safe. The orchard owners are calling their crop insurance company today after an overnight frost killed nearly 10 percent of the apple and three percent of the peach blossoms.
  • Staff photo by Bob Hammerstrom

    Peach trees at Brookdale Fruit Farm will lose approximately three percent of their crop this year after a hard frost overnight Tuesday, March 27, 2012. Orchard owners are checking for a black color inside blossoms, to determine if they have frost damage.
  • Staff photo by Bob Hammerstrom

    Rick Hardy, left, and his brother, Chip look over apple blossoms in the orchard Tuesday, March 27, 2012, at Brookdale Fruit Farm in Hollis. The orchard owners are calling their crop insurance company today after an overnight frost killed nearly 10 percent of the apple and three percent of the peach blossoms.
Wednesday, March 28, 2012

Warm weather made fruit trees bud early, turning seasonal frost into a danger

When you were basking in record warmth last week, farmers were worried. They knew the abnormal weather was making some plants vulnerable when seasonable weather returned.

On Monday night, their fears were realized.

“It got down to 21 degrees in some spots. On apples, we could have lost as much as 10 percent,” said Chip Hardy, owner of Brookdale Fruit Farm in Hollis. “If it had gotten down to 15, we could have lost 90 percent, so we were lucky it didn’t get that cold.”

The problem is that trees and bushes were fooled by a stretch of 80-degree days last week, producing their flowers roughly a month earlier than usual, leaving frost-sensitive buds exposed.

Fruiting plants from apple and peach trees to blueberry bushes and grape vines are vulnerable, as are some decorative plants such as magnolia trees.

“I’m also worried about your hardwood trees that have started to grow buds,” said George Hamilton, UNH Cooperative Extension educator. “I don’t know what the critical temperature is that kills those new growths.”

Critical temperature – the temperature at which a certain percentage of buds or flowers die after 30 minutes – has been measured by agriculture officials over the years, calculated for both “10 percent kill” and “90 percent kill,” for a variety of crops at a variety of stages.

Brookdale’s apple trees, for example, could have handled 15 degrees with only a 10 percent kill rate when buds just came out, but now they’re at the “half-inch green” stage, during which 15 degrees will kill virtually all.

By the time they’re in what is known as first bloom, even 24 degrees will kill 90 percent of blossoms.

That’s why farmers are still worried. It will be many weeks before they can rest assured that no killing frost will come at night, but buds will keep developing, becoming more vulnerable during that period.

“Usually right now, the buds would be dormant,” Hardy said. “The main concern is it’s so early in the season. We have four more weeks (of possible frost) to worry about.”

Similarly, strawberry growers are trying to decide whether to leave protective straw on their rows of crops when the warm weather tempts them to remove it, helping the berries turn red early.

Traditionally, New Hampshire growers consider there to be a 50/50 chance of the last “killing frost” happening as late as May 20, and the advice is not to plant extremely temperature-vulnerable plants before June.

There’s no practical way to protect trees and large-scale fruit production.

Florida growers, for example, use smudge pots to heat orange groves when a rare frost approaches, but that expensive and time-consuming process is worthwhile because frost can kill an entire orange tree, not just buds, Hamilton said.

Similarly, places that use overhead irrigation systems can, in some circumstances, cover buds with water that freezes into a protective shell, but that’s unlikely to apply to most New Hampshire farms.

More worrisome are predictions that weather will become more erratic as the climate warms, leading to more precarious growing seasons down the road.

“Two years ago, you were talking to me right now and I was saying we had to go back to the mid-1940s to find such an early warm spell, but this year is much worse,” said Hamilton. “We got by yesterday … but overall we’re just sneaking by.”

David Brooks can be reached at 594-6531 or