How to Protect Plants from Frost and Freeze
A forecast low near freezing is a cue to check which crops are exposed and whether they need protection. NOAA's tables distinguish 36 °F frost, 32 °F freeze and 28 °F hard freeze. Those are weather thresholds; the temperature that damages a plant depends on the crop and conditions.
Covering a garden bed
North Carolina Cooperative Extension recommends these steps for a cold night:
- Water plants before freezing temperatures arrive.
- Drape a frost cloth or sheet over the plants. Do not use a plastic tarp as the cover.
- Extend the cover all the way to the ground and secure it with bricks or staples.
- Mulch around roots to reduce temperature fluctuation.
- Move container plants into a garage or another enclosed structure for the night.
The same Extension article advises covering semi-hardy vegetables when temperatures are forecast below 30 °F, and hardy crops when temperatures are forecast below 25 °F. It describes these as crop-protection thresholds; they are not the same as NOAA's weather labels.
Read the forecast and crop list together
NC State's freeze terminology uses 36 °F for frost, 32 °F for freeze and below 28 °F for hard freeze. North Carolina Extension notes that freeze-sensitive plants include warm-season crops, while semi-hardy and hardy vegetables tolerate different amounts of cold. See frost-tolerant vegetables for the two Extension lists side by side.
Use the first-frost date tool to understand the local climate-normal dates, then use the current forecast as the event approaches. A station normal is not a forecast for tonight, and a covered plant may still respond differently from the station reading.
Sources
- N.C. Cooperative Extension, Madison County, How Do I Protect My Garden From Frost?.
- NC State Extension, Interpreting Freeze/Frost Probabilities, for frost, freeze and hard-freeze thresholds.
- NOAA National Centers for Environmental Information, U.S. Climate Normals 1991–2020.