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Row covers are commonly used to protect tender vegetables and other plants from fall and spring frosts. Plants are better protected when the cloth cover reaches the ground.
Photo by S. Cory Tanner
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Nursery plant containers make good covers for small plants in a pinch. Make sure to weight them with a rock or brick to prevent wind from blowing them away.
Photo by S. Cory Tanner
What’s not to love about fall in the South? Summer’s oppressive heat and humidity give way to cooler nights, drier air and changing leaf colors. While we relish a comfortable return to outdoor gardening, fall reminds us that frost is right around the corner and, with it, the inevitable end to the growing season.
Many of our warm-season plants delight in moderate fall temperatures. Late plantings of vegetables, such as tomatoes and peppers, really shine in this season of change. Annual flower and foliage plants like petunia, zinnia and coleus and even tropical perennials like elephant ears and hardy bananas excel in the fall. It’s a shame to lose them to an early frost right at their peak.
A little proactive protection can help prolong summer color a bit. First, start paying close attention to weather forecasts for frost advisories around mid-October. The first frost usually arrives between Oct. 15 and the second week of November in the Upstate. Coastal areas south of Charleston may remain frost-free until Christmas.
Once a frost is forecast, make preparations to protect tender plants. Covering, when done correctly, is the simplest and most effective means of protection for short-term frost events (one or two nights). The best covers are fabric materials like cloth sheets, burlap, quilts and commercial frost blankets. They should be large enough to cover the plant to the ground. Covers draped on plants without making contact with the soil will provide slight protection, but they’re more effective when they enclose the plant fully to the soil. Soil holds heat gathered from the sun. At night, that heat is radiated back to the air. Covering a plant to the soil surface traps the heat around the plant and provides several degrees of frost protection. A cover that leaves gaps between the soil and the cover loses much of that insulating potential.
Try to avoid plastic sheeting as a covering material. Plastic robs heat from plant shoots, causing frost burn wherever it touches. If plastic is all you have, suspend it above the plant canopy. Also, plastic must be removed or ventilated during the sunny parts of the day to avoid overheating. Cloth covers may be left on all day, which is helpful for multiple nights of frost.
For small plants, I use what gardeners have in abundance: garden pots. Black plastic nursery pots work great on small plants and transplants, so long as the plastic doesn’t contact the plants. Pots made of clay and other materials also work well. These are my go-to protection for tender vegetable transplants in the spring when a late frost is predicted. Use a brick or rock to anchor lightweight containers, so they won’t be blown off the plant by wind.
You can also use an incandescent lightbulb under cover to add heat on colder nights, and you can wrap tender plants with white Christmas lights (the incandescent types; LEDs don’t produce enough heat). Leaving the lights on overnight may provide enough heat to prevent frost damage. These strategies are helpful for protecting individual, high-value plants.
Finally, don’t attempt the irrigation method of frost protection. You may have seen this used on fruit crops in the spring, but it is very difficult to do and will likely cause more harm than good if not done correctly.
S. CORY TANNER is an area horticulture agent for Clemson Extension based in Greenville County. Contact him at email@example.com.
Forecast: frost or freeze?
What does it mean for your garden if weather advisories call for a frost or a freeze?
A frost can occur at temperatures between 36 F and 32 F under the right conditions. Even a light frost can damage or kill tender plants like tomatoes, basil and coleus.
A freeze occurs at 32 F and below. Temperatures below 24 F are considered a severe or “hard” freeze. A freeze brings a definitive end to the growing season.