Freeze alert: What about the plants?

Freezing temperatures will return tonight - after taking a spring break of more than two weeks.

Temperatures should dip into the mid 20s around Philadelphia - and even into the mid-teens in areas to the north, according to the National Weather Service.

That's flirting with record cold. The historic low is 21 for March 27 in Philadelphia.

The chilliest night so far this month was the 29 reached March 6.

The biggest threat, however, is probably to early drivers, who might encounter icy roads. Temperatures should rebound into the 40s tomorrow.

Tomorrow night, although less chilly, but could see near-freezing temperatures in the city, down to the mid-20s in the burbs and beyond.

Crops aren't really in danger tonight, according to Scott Guiser, an educator with the Penn State Extension Service in Bucks County. Peaches and strawberries, for example, are weeks away from blooming.

Cherry and magnolia blossoms, though, might take a beating.

And so would any houseplants or potted seedlings gardeners might forget to bring inside, Guiser said.

The normal low for late March is in the high 30s, with a normal high around 55, but colder spells are not unusual.

"We'll have many more freezes before we're frost-free," he said.

On average, the last frost is around May 5 for the Philadelphia area, with May 15 a safe date in 9 out of 10 years, said Guiser, who just wrote about crabgrass and baseball in his gardening blog, http://BucksHort.blogspot.com.

Rain Sunday afternoon should accompany temperatures back in the 50s, followed by an overnight low in the 40s. More rain is expected Monday.

For more on the forecast, go to http://weather.philly.com.

To check road conditions, go to http://go.philly.com/traffic.