On spring nights when the atmosphere suddenly retrogrades to January, Meagan Hopkins-Doerr has a reliable arsenal of low-cost supplies for protecting her precious plantings.

“I grab things from the closet,” said Hopkins-Doerr, master gardener program coordinator at the Penn State extension in Chester County. Over larger areas in her garden, she says, spare bedsheets can make fine coverings.

Given the forecasts, one might think electric blankets might be a better option. Temperatures are forecast to fall deeply into the 20s Monday and Tuesday mornings throughout the region — even at freeze-resistant Philadelphia International Airport, with stinging, drying winds. Expect those precocious daffodils to take on that defeated look, says Longwood Gardens horticultural specialist Peter Zale.

After spending most of the winter snubbing local snow lovers, the polar vortex is about to mute those cherry and magnolia blossoms and assorted blooms that were emboldened to open during what has been a remarkably warm March. The March 1 to 21 period in Philadelphia, with an average temperature of 48.7 degrees, constituted the eighth-warmest first three weeks of March in records dating to 1874.

Back-to-back days with highs in the mid-70s last Friday and Saturday “definitely pushed a lot of things,” said Jeff Lynch, grounds manager at Chanticleer Garden, located in a pastoral stretch of Church Road in Wayne where it tends to get colder than the airport, which would not be good for the welfare of the early bloomers.

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“They’re going to need protection,” he said. Forget the electric blanket by the way. A sheet is a way better option, or burlap, or some other porous material: Plants have to breathe. And you might want to keep those covers handy.

Those rains Wednesday night and Thursday signaled that nature hadn’t quite yet flipped the switch to spring, and the government’s Climate Prediction Center’s outlook through April 8 has odds favoring below-normal temperatures in the region.

‘There’s no normalcy’

Overall, the blooming and tree-leafing around Philadelphia appears to be well ahead of schedule, according to those who make a living caring for them. The magnolia and cherry blossoms might be a week ahead, said Zale, who is Longwood’s associate director for conservation, plant breeding, and collections.

The daffodils typically peak in early April, he said, but those golden trumpets appear to be at full volume around the region. The snow drops, usually toast by now, are hanging tough.

But the trend hasn’t been uniform. Some plants, such as the skunk cabbages, are behind, Chanticleer’s Lynch said. Last weekend when he was at the New York Botanical Garden, 100 miles to the northeast, he noticed that the corydalis were blooming ahead of those around here.

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Perhaps the plants have been as confused by the atmosphere as their human caretakers. While March has featured six days with highs above 70 degrees in Philly, lows were in the 20s four times. Last month temperatures were close to 4 degrees above normal, but on five occasions daytime highs were 20 degrees different from the previous day, something that has happened in only eight other months in the period of record.

“There’s no normalcy anymore,” said Lynch.

First and last freeze dates bounce around from year to year, but there’s clear evidence the growing seasons have been growing, a by-product of a changing climate. On Thursday grass pollen appeared earlier than it ever had in his more than three decades of pollen-counting, said allergist Donald Dvorin, who practices in Mount Laurel, Burlington County.

It is likely that the official maps showing which areas are most favorable for certain plants “will start to be reevaluated,” said Hopkins-Doerr, who also is the master watershed steward coordinator for Chester and Delaware Counties.

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She holds training sessions in March and April for live-staking, an erosion-control process in which branches are cut from trees while they are still dormant, when they have the most energy. Once planted on creek banks, they grow roots. With all the recent warm days, she is concerned the red osier dogwoods, a primary source for the branches, will be leafing earlier than usual this year and in future years.

“I may be looking at doing workshops in February next year,” she said.

This coming chill

We might get a taste of what already has happened to our South, Lynch said. On March 12 and 13, temperatures dropped into the 20s in Atlanta, zapping the tulips, and in Washington, targeting the magnolias.

Washington’s legendary cherry blossoms reached peak last week, but they, too, will be taking a hit.

Around here, the trees already hosting blossoms are likely to take on quite a different look with the start of the workweek. The 25- to 30-mph winds will intensify the winter-like dryness, said Zale, and be especially punishing for the blooms: “It can suck the life out of them.”

The daffodils will be hanging their heads, but they will recover. “They get right back up,” Zale said, albeit with some lost vigor. “They’re not going to look as fresh.”

He added, “The trees will be fine.” They’ve been through this drill, he said: Post-bloom freezes are more the rule than the exception.

In addition to using bedsheets, home gardeners can guard delicate plantings with fabric, mesh, or burlap coverings, providing the temperatures don’t get too low.

“If it gets down to 22,” said Lynch. “There’s not a lot you can do.”