Flowers that may be damaged by frost should be covered or brought indoors tonight.

Cover your petunias, we’re looking at a possible frost just days before the unofficial planting season begins.

Tom Green, a meteorologist with the National Weather Service, said conditions late Friday night and into Saturday morning will be in the zone for frost.

“All of Butler County will be at risk for a frost, but it will be more so north where the low temperature is expected to be around 31 or 32 degrees at the Venango County line,” Green said. At the Allegheny County line, the low temperature is expected to be about 34 or 35 degrees.

Depending on humidity and wind either temperature could accommodate frost, Green said, noting that while warm air rises cold air tends to settle in dips and valleys making them even more susceptible. Frost, in a basic sense, is humidity that cooled and settled onto the ground.

“This is really unusual,” Penn State Master Gardener Justine Brown of Butler said of the late day of the frost.

Memorial Day, the last Monday of the month, is nearly a week earlier than it could be if the calendar had stacked up differently, as it has in the past.

“Typically we in Zone 5 say Memorial Day is the day you should be able to put your plants out without a fear of frost ... but it normally doesn’t occur this late. And if you would have asked me last week, I would have said it would be OK to start planting with the warm temperatures and the long-term outlook.”

A lot of people locally did use the sunny days to decorate the yard. But the expected frost could burn or damage sensitive annuals, like tomatoes and peppers.

Frost damages plants when the sun comes out and melts off the solidified dew. So a gardener could go out in the morning before the sun gets hot and spray the frost off with a hose to mitigate damage.

However, an ounce of prevention is easier and more affective.

Brown said throw a towel or sheet light enough to prevent weight damage onto sensitive plants. If you planted in containers, move them into the garage or under a porch.

Don’t use plastic bags, they won’t insulate against frost, and don’t worry about cold weather loving crops like asparagus, cabbage and swiss chard.

“There’s a lot of micro climates within our climate so if you know your yard to be a little cooler, take extra precautions,” she said.