The National Weather Service issued a frost advisory for parts of Virginia and Maryland on Sunday, warning that “sensitive outdoor plants may be killed if left uncovered.” Temperatures could dip to the low to mid-30s between 3 a.m. and 9 a.m. Monday.

In the Washington region, the advisory included Loudoun, Fauquier, Frederick, Carroll and Baltimore counties. National Weather Service meteorologist Kevin Witt said other areas could be added as conditions evolve. “Right now, Montgomery’s a maybe,” he said.

Depending on the plant, a blanket could help, according to Francesco DeBaggio, owner of DeBaggio’s Herb Farm & Nursery in Chantilly. “If frost forms on the leaf, it’ll burn that leaf, it’ll burn that tissue,” DeBaggio said. “The blanket would protect that from frost.”

Still, “if it’s a plant that’s going to be just hurt by cold, you kind of have to cross your fingers,” DeBaggio said.

Zinnias, with their colorful blooms, don’t like the cold, he said. Other heartier plants, such as parsley, could be in trouble if they were recently transplanted from a greenhouse, he said.

Many people plant tomatoes, peppers and basil too early and frost is only part of their problem, DeBaggio said. Mid-May, when temperatures are settled in the mid-50s, is a better planting time, he said. While a blanket or other cover could prevent frost, it might raise the temperature by only a couple of degrees. That’s not enough to protect a tomato plant from a blast of cold that may leave no visible scar but could stunt its performance later on, he said.