Gardening Tips and Highlights Waushara County Master Gardeners

Defend against late frosts

by Christine Yesko               


In regions with cold winters where frosts occur and the ground freezes, there’s a typical last frost date. This is the date in spring by which you can somewhat safely assume no more frosts or freezes will occur until fall. You can find out this date in your area by checking with your local co-operative extension office or asking experienced gardeners in your neighborhood.

Frosts can and do occur after the last frost date; however, there are strategies for coping with a late frost.

Protect plants from cold snaps. Avoid planting tender plants in low-lying areas. There are frost pockets, which is where cold air drains on radiational cooling nights-clear, calm nights when the heat rises from the earth’s surface and cold, denser air sinks down. Plant marginally hardy trees, shrubs, and perennials where they will be protected from winds, such as behind a row of evergreens.


Plant them near a wall or building and they will receive extra warmth from it. Watch weather reports for frost watches and warnings. Clear skies, a lack of wind, and a chilly afternoon generally precede a night with a drastic drop in air temperature. On a clear night, the dew point can be a good indicator of how low the temperature will get by morning.

If a light frost is predicted, drape tender plants, newly planted perennials and anything with sensitive new growth or flower buds with old bed sheets. If a killing frost is predicted, prop the sheets upon stakes so that they don’t touch the foliage, and pin down their edges with stones or bricks. The sheets trap warm air, preventing it from radiating into the atmosphere. Move container plantings to a sheltered but unheated location, such as on a porch or into a garage or shed.

If potted plants have been left out and are affected by frost, don’t try to warm them by bringing them indoors, the sudden change in temperature would damage them further.


This information was obtained from the Horticultural Magazine.