Yes, frost covers for plants work very well when used the right way. A good cover gives your plants 4 to 8°F of extra warmth on a cold night. This buffer is enough to save most tender crops from a light to moderate freeze.
I tested frost cloth on my tomato plants one fall when the forecast called for 28°F (-2°C). The plants under the cloth came through the night with zero damage. The same kind of tomato in the next row without a cover turned to mush by morning.
The science behind covers is simple. Your soil soaks up heat from the sun all day long. At night, that heat tries to rise into the cold sky above. A layer of frost cloth stops the heat from leaving and holds the warm air close to the plant.
Think of the cover as a thin blanket for the soil. It blocks the sky and traps the warmth right around the leaves. Plain bed sheets work the same way but with less power. UC Master Gardeners in Sacramento show that purpose-made cloth gives 4 to 8°F of buffer. Missouri Extension lists plain blankets at only 2°F of help.
Frost blanket effectiveness comes down to weight and weave. Heavier cloth traps more heat but blocks more light. Lighter cloth breathes better but offers less buffer on the coldest nights.
Light Weight (0.5 oz per square yard)
- Protection level: Buffers 2 to 4°F above the air temperature on a still night.
- Light passage: Lets through 70% of sunlight, so you can leave it on for days at a time.
- Best use: Spring frost on young seedlings and light fall freezes on lettuce or chard.
Medium Weight (1.0 oz per square yard)
- Protection level: Buffers 4 to 6°F for most home garden needs through the cold season.
- Light passage: Lets through about 50% of sunlight, good for short stints on plants.
- Best use: Tomatoes, peppers, and citrus in zones 7 through 9 during fall and spring.
Heavy Weight (1.5 oz per square yard)
- Protection level: Buffers 6 to 8°F on the coldest nights when you need full power.
- Light passage: Lets through only 30% of sunlight, so pull it off during the day.
- Best use: Hard freeze events below 25°F (-4°C) on small fruit trees and shrubs.
Pick a weight that fits your zone and the plants you grow. I keep both light and medium cloth on hand for most fall and spring nights. The heavy stuff comes out only for the deep freeze warnings that hit a few times each winter.
Drape the cloth all the way to the ground around each plant. This traps the warm soil heat down low. Leaving gaps at the base lets cold air in and ruins the buffer effect you want.
Pull the covers off on sunny mornings once the air warms past 40°F (4°C). Heavy cloth can cook your plants if you forget on a warm day. The small daily habit of cover and uncover is worth the work for the crops you save.
Read the full article: Frost Protection for Plants: Complete Guide
