Last Updated on October 8, 2026

How to Protect Plants from Frost

Cover tender plants in the evening as the sun sets, so the cover traps the heat the soil stored during the day. Take the cover all the way to the ground, hold it off the leaves, weight the edges, and take it off the next day once it is above freezing. Frost cloth, row cover, old sheets and blankets all work; just keep sheets and blankets dry. Covers buy a few degrees: frost blankets and row cover generally add 3 to 5°F, and below about 28°F a cover alone usually is not enough. For tomatoes, peppers and other tender crops, pick what you want to keep when the low will be 32°F or colder.

Which crops need a cover at which temperature is in my vegetable frost tolerance chart. In short: cover tender crops like tomatoes, peppers, beans and squash when the forecast low is 36°F or colder, semi-hardy crops below 28°F, and hardy crops below 24°F.

How to cover plants for frost, step by step

1. Water the soil the day before. My fall crop planting guide says to water the soil around your plants a day before an expected frost, because moist soil absorbs and holds heat better than dry soil.
2. Set up supports. Iowa State University Extension suggests stakes, posts, PVC pipe, patio furniture, sawhorses or wire loops to keep the cover off the foliage.
3. Cover in the evening, as the sun sets. Put the cover on as the temperature starts to drop, so it holds in the heat radiating from the ground.
4. Take it all the way to the ground. University of Florida IFAS Extension says a cover must reach the ground to trap the heat coming off the soil.
5. Weight the edges. Utah State University Extension weights covers with bricks or stones, or anchors them to the soil, and checks that there are no openings where heat can escape.
6. Uncover the next day. Iowa State says to remove the covering once it is above freezing.
7. Repeat as needed. Iowa State notes that a below-freezing night is often followed by a week or more of warmer weather, so covering through a cold night can stretch the harvest.

What to cover plants with for frost

Heavier fabric holds more heat but lets in less light (90 to 95 percent for lightweight, 30 to 50 percent for heavyweight, University of Maryland). Sheets, blankets and plastic come off every morning; lightweight row cover can stay on some crops from seeding to harvest.

Keep plastic off the leaves: Utah State warns that leaves touching plastic can freeze. Plastic also overheats fast, and Colorado State says it can top 130°F under a closed cover after just an hour of sun.

Is tonight a frost night?

The forecast low is the first clue. Iowa State says the National Weather Service issues frost advisories when lows are forecast between 33 and 36°F. Four things raise the odds.

• A clear sky. Colorado State says radiation frosts come on calm, clear nights with no cloud cover to hold in heat.
• Calm air. Calm to light winds let a thin layer of very cold air form right at the surface (National Weather Service, La Crosse).
• Dry air. South Dakota State University Extension says frost is more likely when the dew point is below 32°F, especially in dry air.
• A low spot. Nebraska Extension says cold air pools in the lowest parts of a yard, so plants there are more likely to be damaged.

That gap is why frost can form on a 36°F night. The National Weather Service in La Crosse gives that exact case: a 36°F reading, with the air touching the ground at 30°F or colder.

When covering is not worth it

Covers buy a few degrees. When the night needs more than that, harvest instead.

• Tender crops at 32°F or colder. The frost tolerance chart says tomatoes, peppers and other tender crops do not tolerate freezing, so pick what you want to keep when the low will be 32°F or colder.
• Below about 28°F. Iowa State says covering is typically no longer effective at preventing cold damage once temperatures drop below about 28°F.
• Semi-hardy crops on a cold night. For semi-hardy crops, which the chart says to cover between 24 and 28°F, use the heaviest cover you have: University of Maryland Extension gives up to 8°F for heavyweight row cover. Or use a cold frame.
• A long cold night. Iowa State says plants can be damaged under a cover even above 28°F when below-freezing temperatures last 5 hours or more.
• A windy cold front. Colorado State says these advective frosts can drop well below the point that damages plants, which makes protection questionable.

On those nights, pick the tender crops first. For tomatoes, pick the mature green fruit and ripen green tomatoes indoors. Nebraska Extension says to pick peppers before frost if you cannot cover them, and to harvest winter squash and pumpkins meant for storage before frost, because frost damages the rind and shortens storage life. Hardy crops like kale, collards and cabbage can often ride it out uncovered; the frost tolerance chart has the line for each crop.

To keep cool-season crops going longer than a cover allows, use a structure. My cold frame tips cover where to put one, venting it on warm days, and adding bubble wrap, row cover fabric or old blankets on cold nights.

Pots and containers: move them or group them

Iowa State calls bringing plants indoors the easiest protection: pull potted plants into a heated room, a porch or a garage for the night. For pots that stay outside, UC Marin Master Gardeners say to cluster them close together, in a sheltered spot near the house if you can. Check them again later: UF IFAS says cold injury to the roots of potted plants is common and usually does not show until warmer weather.

Mulch is for what is in the soil, not a frost cover for leaves; UF IFAS says mulch around plants reduces heat loss and protects the roots, and my fall crop planting guide uses straw, leaves or compost as an insulating layer.

My fall gardening checklist brings some herbs and peppers indoors for the winter, and my guide to overwintering pepper plants says to start planning once nights dip below 50°F and bring them in before any frost damage.

The morning after a frost

• Let frozen plants thaw first. Iowa State’s low tunnel guide says cool-season crops cannot be harvested while frozen, so wait until they thaw, which usually means late morning.
• Read the damage. SDSU Extension says frost injury is usually shallow: bronzed or bleached patches, burned leaf edges and small dead spots. Freeze injury goes deeper: tissue looks water-soaked or see-through, goes limp after thawing, then turns brown or black.
• Give hardy crops a week or two. Iowa State’s cold damage guide says radish, lettuce, chard and onion take minor damage below 32°F and readily recover within 7 to 14 days. Spinach, beets, collards, kale, carrots, cabbage and Brussels sprouts usually take only minor damage, if any, down to 28 to 26°F.
• Water pots after a freeze. UF IFAS says watering helps frozen container soil thaw and the plants rehydrate.
• Pick what got hit, fast. Nebraska Extension says frosted peppers turn mushy and rot quickly, bean pods do not show the damage right away but should be picked and used soon, and summer squash deteriorates quickly. Frosted winter squash and pumpkins should be picked within a day or two and cooked, frozen or canned right away.

Once frost has killed the tender crops, I cut them at the soil line and leave the roots in, send the tops to the compost pile, and lay two inches of compost on the empty bed.

Quick questions

What is the best thing to cover plants with for frost?

Frost cloth or row cover, held off the leaves on hoops or stakes and weighted to the ground. Old sheets and blankets work if they stay dry. Plastic works only if it does not touch the leaves and comes off the next morning.

What time should I cover my plants for frost?

In the evening, as the sun sets and the temperature starts to drop, which is when my fall crop planting guide says to cover your crops. Take the cover off during the day.

Can I cover plants with plastic or trash bags?

Yes. Nebraska Extension says caged tomatoes, peppers and eggplant can be covered with paper grocery sacks or plastic trash bags, and that plastic has to come off the next morning or the plants may cook in the sun. Keep the plastic from touching the leaves.

Should I water plants before a frost?

Yes, water the soil the day before. My fall crop planting guide says moist soil absorbs and holds heat better than dry soil.

Can it frost at 36 degrees?

Yes. The National Weather Service in La Crosse says temperatures are typically measured 4 to 5 feet above the ground, and on a calm night the air at the surface can be up to 10 degrees colder, so a 36°F reading can mean 30°F or colder at your plants.

Know when your first frost is due

Frost protection starts with knowing when frost usually arrives where you live. Enter your zip code on Plan My Garden and it finds your frost dates, including your first fall frost. Plan My Garden is free to start: enter your zip code, draw your beds, pick kale, lettuce, tomatoes and everything else you want to grow, and it places each plant at square-foot spacing and builds a planting schedule (start indoors, transplant and direct sow dates) from your frost dates.

Related: Vegetable Frost Tolerance Chart · How to Ripen Green Tomatoes Indoors