What’s behind the leaf explosion? Why the region suddenly has turned green

April is busting out all over with an explosion of green the last few days.

If it appears as though the trees suddenly have awakened, that’s because they have.

In just the last few days, leaves have been popping and a green haze has washed over the woodlands across the region.

“It seemed like everything jumped forward,” said Peter Zale, curator at Longwood Gardens, in Kennett Square.

“It really does seem to be concentrated,” he said, adding that some longtime local gardeners have told him “they’ve never seen anything like this.”

The explosive behavior of the region’s arboreal life is directly related to one of the stranger four months in the region’s weather history.

Trees and other plant life were exhibiting a certain precocity in February, when for the first time in records dating to 1874 the temperature hit 70 or better on four different days.

The warmth lapped into March, but the seven-day period from March 11 through 17 marked the second-coldest period of the year, barely out-chilled by the Jan 5-11 period, and colder than any week in December.

Kennett Square, said Zale, recorded its coldest temperature of the winter during that week in March, and you might recall that was the week of the season’s most-significant winter storm and the same week that Gov. Christie declined to give the National Weather Service a hug.

The cold spell cost some trees and other plants their blossoms. “Some of them got nipped,” said Zale.

It took awhile for April to get cooking, but in the week from Monday through Easter, the temperature reached 80 three times, peaking at 87 on Sunday.

The leaves, obviously, have decided it’s safe to come out now. And so has the pollen.

The tree-pollen count on Monday reached the "extreme" level, according to the Asthma Center.

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