Frost on the pumpkins may conjure up images of bountiful harvests and fall festivities, but when frost arrives in late spring it takes on a more ominous meaning. According to Ron Wolford, a horticulturist at the University of Illinois Extension Services, frosts kill plants when internal temperatures drop causing plant cells to break down or burst. Protecting tender plants from late spring frosts requires maintaining adequate air temperature around the plant. This can be accomplished in several ways.
Water plants thoroughly the day before an expected frost. Wet soil retains more heat and is often 2 to 4 degrees Fahrenheit warmer than dry soil. Heat trapped in the soil is released at night providing protection against frost.
Cover tender crops with plant caps, sheets or tarps to provide a barrier to frost and to hold in radiant heat from the soil. Cut the bottoms off milk cartons or large plastic bottles for a quick cover for young plants. Place soil or rocks around edges to secure in place and prevent blowing. Remove in morning once the air has warmed.
Suspend row cover over plants when frost threatens. Install with the appropriate hardware and follow instructions included with the row cover. Leave row cover in place during the day, as it allows water and sunlight to penetrate. Remove when plants are established and all danger of frost has passed in your area.