August 30, 2026 · Updated September 13, 2026
How to protect plants from a freeze
A light frost and a hard freeze call for different covers, so size your protection to the low your own yard will hit tonight instead of the number in the regional warning. Find your real low, match it to how cold each plant tolerates, and cover only the plants that fall below their threshold.
Frost and freeze are different events
A frost forms when a plant radiates its heat to a clear sky on a still night. The leaf surface drops below freezing and water vapor freezes onto it while the air a few feet up can still read above 32°F. A freeze is colder weather across the whole air mass. The air itself falls below 32°F, and ice forms inside plant tissue and breaks the cells. A cover fights the first by trapping ground heat under the plant. It buys you only a few degrees against the second.
How cold it takes to hurt a plant
Tender summer crops take damage at or near 32°F. Tomatoes, peppers, cucumbers, and squash sit in this group. Hardy greens and roots hold much lower. Kale, spinach, and carrots ride through the low 20s and often past it. Before you cover anything, read each plant's rating against your yard's real low, which our guide on frost-resistant plants and your real low walks through.
Steps to protect plants from a freeze
- 1. Find tonight's real low. Regional forecasts describe conditions at the airport. Cold air is denser, so on still nights it drains downhill and pools in low spots, which run colder than the published number.
- 2. Sort your plants by threshold. List which beds hold crops that drop below their rating tonight. Leave the hardy ones uncovered.
- 3. Choose breathable fabric. Frost cloth, a sheet, or a light blanket traps rising soil heat and lets moisture escape. Skip plastic against foliage, since it conducts cold straight through the leaves it touches.
- 4. Cover before sunset. The ground gives back its stored heat all night, so draping the cover while the soil is still warm holds that heat around the plant.
- 5. Uncover in the morning. Once the air climbs back above freezing, pull the cover off so the bed does not overheat under sun and the plant gets light.
The cover only works if it reaches the soil on every side. A cloth draped over foliage alone leaves the warm ground sealed off below it, and the plant loses heat to the sky as if it were bare.
What can go wrong
Two mistakes waste the effort. Fabric held up on the leaves by nothing but the plant conducts cold at every contact point, so tent it on stakes or hoops. And a cover cannot revive tissue that already froze, nor does it help roots in a bed that stays frozen for days. On a hard freeze, warm the ground first: water the bed in the afternoon, because moist soil stores and releases more heat overnight than dry soil. Our note on watering before a freeze covers which nights that pays off.
The gap in every plan is knowing your own low. Our station sits about 7°F below the forecast on still nights. Last fall the first frost hit our beds on October 3, while the published date for our area came weeks later, on October 22. A free Siltwell account lets you enter your own offset in Settings, and every alert then works from that figure. A connected station on Pro learns that offset after about 14 overlapping nights and adjusts frost alerts to your site. Run the microclimate checker before you commit. It holds the forecast low against readings nearby home stations logged on recent nights, which shows how far your yard drops below the regional figure.
Common questions.
- How do you protect plants from a freeze?
- Find the low your own yard will reach tonight, match it to how cold each plant tolerates, and cover the tender ones with fabric that reaches the soil. Put the cover on before sunset so it traps the day's ground heat, and take it off once the air rises above freezing the next morning. Plants rated colder than your low need nothing.
- What is the difference between a frost and a freeze?
- A frost forms when a plant's surface radiates its heat to a clear sky on a still night and drops below freezing while the air can still read a few degrees above 32°F. A freeze happens when the whole air mass falls below 32°F, so ice can form inside plant tissue and rupture the cells. Frost damages exposed leaves; a hard freeze reaches stems and roots.
- What is the best thing to cover plants with during a freeze?
- Breathable fabric works best. Use frost cloth, an old sheet, or a light blanket that drapes to the ground and traps rising soil heat. Plastic sheeting conducts cold straight through wherever it touches a leaf, so keep it off the foliage if you use it at all. The cover has to reach the soil to hold heat around the plant.
- How cold does it have to be to damage plants?
- Tender summer crops like tomatoes, peppers, and cucumbers show damage at or near 32°F. Hardy greens and roots such as kale, spinach, and carrots hold through the low 20s and often lower. Match each plant's rating against your yard's real low before you decide what to cover.
Related guides
How to protect tomato plants from frost
Learn why a light frost kills tomatoes, why your yard freezes before the forecast, and which nights to cover.
Can plants recover from cold shock after a frost night
How cold shock kills plant tissue, how to tell what survived, and when to prune, water, and feed a cold-damaged plant.
How to protect plants in winter without covering every night
Learn which winter nights actually threaten your plants, how cold triggers a cover, and how a learned frost offset tells you your yard's real low.
Free planting tools
- When to plant shows the last date to sow each crop before your fall frost.
- Microclimate checker shows how much colder or warmer gardens near you ran than the forecast low.
- GDD estimator adds up a typical season's heat and shows which crops can ripen where you are.
