Freeze forecast in Washington region threatens tender plants

And now, back to your regularly scheduled weather.

After all those unseasonably warm temperatures briefly turned Washington into Waikiki and tricked daffodils and day lilies and the like into thinking spring was well underway, a chilling correction is coming: The National Weather Service has issued a freeze watch for late Monday into Tuesday morning for most of the region.

Hide the hostas and newly planted impatiens, the Weather Service said (sort of), because the Arctic air mass pushing down from Canada might cause “widespread freezing temperatures” in the Washington area, which might “damage sensitive vegetation,” of which there is more than usual, after the recent heat wave pushed soil temperatures into the 50s , well above normal.

“This year is crazy,” Alex Dencker said Sunday at the Behnke Nursery in Potomac, where he was thinking about the 10-by-50-foot protective rolls he’d have to spread over thousands of confused plants beginning Monday afternoon. “I’ve never seen roses with this kind of growth. Lilacs, crape myrtle, peonies — all this stuff has growth on it that easily looks like mid-April. So this little cold snap will be particularly rough.”

But, said Dencker, who manages the six-acre nursery, there’s nothing surprising about a late-March freeze. “If you look at the calendar, it’s quite appropriate,” he said.

The average date of the last freeze in Washington is early April, said Jason Samenow, chief meteorologist with The Washington Post’s Capital Weather Gang.

Of course, this isn’t an average year. Washington’s cherry blossoms peaked Tuesday — five days before the official start of the National Cherry Blossom Festival and the third earliest peak on record.

“People made the assumption that cold weather was done,” Samenow said. But the coming cold front is nothing unusual, he said, adding that it’s a mere “glancing blow” that should be gone as quickly as it arrives: By Wednesday, it’s probably going to be 70 degrees again.

But between now and then: Brrrrrrrr.

Overnight lows are expected to plunge into the lower 30s inside the Beltway and possibly into the upper 20s west and northwest of the Beltway late Monday into Tuesday.

Plan accordingly, gardeners.

“Any new 2012 growth on most plants will be in jeopardy, ” Dencker said. “That foliage has not yet been acclimated to anything below mid-30s.”

Freeze protection 101: Vulnerable plants that can’t be moved inside should be covered with fabric-type materials, Dencker said, from bedsheets to burlap. And try to prop up the covering with sticks, so that its weight isn’t resting directly on the plants.

“I would do it at dinner time,” he said. “It can probably come off by 9 the next morning, when the danger of frost has passed.”

J. Freedom du Lac is the editor of The Post's general assignment news desk. He was previously a Local enterprise reporter and, before that, the paper’s pop music critic.
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