The Homeowners Column

The Homeowners Column

Anticipating Frost - What to Do With Frost Sensitive Plants

Photo of Sandra Mason

Sandra Mason
Extension Educator, Horticulture
slmason@illinois.edu

October 14th should be circled, underlined, highlighted, starred, and asterisked on your calendar. No it's not my birthday, but it is generally considered to be the average date of first frost in our area. First frost has occurred as early as September 22 and as late as November 7 in our area so nature, as usual, keeps us guessing and playing the odds. What does all this mean? Well it means that if you don't want your basil to turn to mush, you better harvest it soon.

A few of the plants that are frost sensitive include ageratum, begonias, impatiens, annual vinca, celosia, coleus, geranium, salvia, zinnia, tomato, pumpkin plants, okra, cucumber, sweet potatoes, tropical plants such as bananas, hibiscus, and elephant ear, and house plants.

We have several options when dealing with frost sensitive plants. We could wait until 10:15 some night. The weather person announces the chance of frost. With flashlight in hand we make a quick round-up of all our houseplants, cover all the tender plants with bed sheets, and harvest all the green tomatoes using our pajamas as the basket. Or we could just shed a tear to another passing summer and let nature take her plants to the happy compost pile in the yard. However, gardeners being gardeners we like to stretch the boundaries and we hate to watch any plant die.

We can pot a few of those tender flowers for winter enjoyment. It's best to get them ready for the trip indoors by potting them early and placing in shady spot for a week. Think of it as a halfway house or Ellis Island for plants. Annual flowers such as vinca, begonia, geranium and impatiens will continue to flower indoors. Not all annuals will flower but can certainly be saved for next year's garden. Coleus also makes an attractive houseplant. Rosemary can take freezing temperatures, but have her potted and ready to go inside once temperatures dip below freezing.

Before bringing plants indoors, check for insects. Some common plant pests include: aphids; scale; whitefly; and spider mites. If insect pests are suspected, plants can the treated with insecticidal soap such as Safer's or Ortho. Insecticidal soaps are specially formulated soaps to be used on plants and have low toxicity. Read and follow all label directions.

It's generally a good idea to wash the leaves and stems of any plants with a steady stream of water before bringing them indoors. With potted plants the constant drenching of the soil will also help to drive out soil critters like pill bugs and ants. Plants can also be repotted with new soil to make sure there are no unwanted guests.

If tender plants such as geraniums and coleus are particularly large, take 4 to 6 inch long stem tip cuttings. These can be rooted in small pots with soiless mix. A plastic bag over the top will keep in moisture. The plants generally root in about 2 weeks.

Seeds of marigolds, celosia, zinnia, and others can be collected. Make sure the seeds have ripened adequately before harvesting which usually means a color change from green to brown. Keep in mind seeds from hybrid varieties generally will not produce plants that look exactly like their parents. Store seeds in refrigerator or other cool, dry place.


Tender vegetables such as peppers, tomatoes, eggplant, and sweet potato should be harvested before a frost. Wrap green tomatoes individually in paper and store at 60 to 65 degrees F. They will continue to ripen slowly over the next several weeks. They do not need sunlight to ripen.

The roots of tender perennials such as dahlia, caladium, canna, and elephant ear should be dug before a hard freeze and stored in cool, dry place. Enjoy the remnants of summer with this beautiful weather.

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