Protect Tender Plants Saturday Night!

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The mild weather of the past few weeks may have tempted us into thinking we had seen the last of winter for the year, but that will change Saturday night when lows are predicted to dip into the lower 20’s across much of central North Carolina. Temperatures this low will damage open blossoms on fruit trees, blueberries and ornamental trees such as saucer magnolia, as well as any freeze sensitive vegetables and annual flowers that have already been transplanted.

N.C. map

Low’s in the 20’s are predicted for much of central N.C. Sunday morning. Source: NC State Extension Strawberry Growers Information Portal

If you succumbed to spring fever during the past few weeks and have already planted freeze sensitive plants such as tomatoes, squash, begonias, or marigolds outdoors, take measures during the day Saturday to protect them. Plants should be covered with double layers of row cover or blankets. Make sure covers extend all the way down to the ground and are securely held down by bricks or staples. Most of the protection provided by covers is from the soil warmth they trap in, which would otherwise radiate out into the night. Any plants in containers should be brought into a garage or other enclosed structure for the night.

If your blueberry bushes have already started to bloom, protecting them by completely covering with old blankets or row cover will likely result in higher yields. If you are not able to protect bushes with open flowers all is not lost. Blueberries do not open all their blossoms at once so if some blossoms are lost this weekend more will likely open over the next few weeks that will result in berries later in the season.

For more tips on protecting plants from freezing temperatures, see this Extension Gardener article.

Exactly What Is a Hard Freeze?

According to Mike Moss, WRAL meteorologist, “There isn’t really a single “official” definition of the term. In general, “hard freeze” is used to imply temperatures that are sufficiently cold, for a long enough period, to seriously damage or kill seasonal vegetation. In our area, this usually means temperatures falling into the upper 20s or lower for at least two to three hours.”

The National Weather Service issues a hard freeze warning when “widespread temperatures below 28° are expected during the growing season”. This differs from a freeze warning, which is issued when temperatures below freezing are expected during the growing season.

Cool season vegetables such as broccoli, garden peas, spinach, cabbage and carrots tolerate temperatures down to 28° and lower and can be planted outside in central N.C. in March. These plants are not likely to be seriously damaged this weekend, unless they have recently been transplanted out of a greenhouse without first being hardened off (gradual exposed to cooler temperatures). In this case, row covers should provide enough protection for recent transplants. Established crops may also be covered to minimize the potential for injury.

Wait until after the average last spring freeze date to plant freeze sensitive warm season crops such as tomatoes, peppers, beans, cucumbers, squash, and corn. The last spring freeze typically occurs sometime between April 1 and April 11 for most of the N.C. piedmont. Any freeze sensitive plants left outdoors Saturday night will be killed unless measures are taken to protect them.

North Carolina spring frost map

Average last spring frost dates for N.C. Source: National Weather Service

Is This Winter’s Last Blast?

Only time will tell if Saturday night proves to be our last hard freeze for the season. The National Weather Service’s Climate Prediction Center predicts an equal chance of April temperatures being either above or below normal for the southeastern U.S.

Gardeners willing to take a risk on losing a few plants may wish to seed or transplant some warm season crops before mid-April, especially in sunny, south facing areas where soils warm early. This gamble tends to pay off more often than not, particularly if you are able to protect plants from light freezes by covering them with row covers. Benefits of early planting include earlier harvest dates, higher yields, and greater production early in the season before insect and pest pressure builds up.

Download NC Extension’s publication on planting dates for vegetables and herbs in central N.C.

Learn More!

  • Many garden centers and online suppliers sell floating row cover – here is one example
  • Cold frames are an alternative to floating row cover. Find out more about building and using cold frames from this Missouri Extension fact sheet
  • Many vegetable farmers use high tunnels, a type of unheated greenhouse, to grow winter crops. If you are serious about growing vegetables year round, consider installing a high tunnel for winter gardening. Learn more about high tunnels from eOrganic

 Extension Fact Sheets on Protecting Landscape Plants from Cold:

Use Extension Search to find research based information from Cooperative Extension systems across the U.S.

Visit your local Cooperative Extension center to learn more about gardening and landscape care. Find your county Extension center.

Subscribe to the Chatham Gardener email list to receive timely updates on sustainable lawn, garden, and landscape care for the central NC Piedmont.