Cover tender plants in the evening when the forecast low reaches the mid-30s °F on a clear, calm night, and take the covers off the next morning once it’s above freezing (Iowa State Extension). Use frost cloth, old sheets, blankets or a cardboard box, held up off the leaves and reaching the ground, so they trap the warmth rising from the soil. Don’t let plastic touch the leaves. Water dry soil a few days ahead. Covers help down to about 28 °F; on a colder night, bring pots indoors and pick what you can.
What temperature is frost?
Frost is ice that forms on leaves and other surfaces when they cool to 32 °F. On a clear, calm night, leaves lose heat to the open sky and get colder than the air around them, so frost often forms while the thermometer still reads in the mid-30s (National Weather Service). The NWS office in Raleigh issues frost advisories when lows of 33 to 36 °F are forecast for a clear, calm night, and notes that frost can form once the air falls below 36 °F, especially in the countryside.
A freeze is when the air itself drops to 32 °F or below. UC IPM puts it simply: in a frost, the air stays above 32 °F but the plants cool below it; in a freeze, the air is that cold too. A freeze can come on a windy night, when a mass of cold air moves in, or on a clear, calm one (Iowa State). The NWS office in Midland, Texas, sorts freezes by how cold they get:
| Night low | NWS term | What it does to plants |
|---|---|---|
| 33–36 °F | Frost advisory | Frost can form on leaves on clear, calm nights. |
| 29–32 °F | Light freeze | Tender plants are killed; little harm to other plants. |
| 25–28 °F | Moderate freeze | Widely destructive to most plants, with heavy damage to fruit blossoms and to tender and semi-hardy plants. |
| 24 °F and colder | Severe freeze | Heavy damage to most plants; the ground freezes solid. |
Frost advisory: NWS Raleigh. Freeze categories: NWS Midland/Odessa. The NWS glossary calls 28 °F or lower for an extended time a hard freeze, which kills most kinds of vegetation.
How long the cold lasts matters too. Iowa State Extension notes that covered plants can still be damaged above 28 °F when it stays below freezing for 5 hours or more. Your own frost dates, and the odds of an earlier or later frost, are on frost dates by ZIP code.
How much cold each plant can take
Plants fall into groups by how much cold they take. The University of Minnesota’s table for fall vegetables gives the temperatures, and Iowa State adds houseplants:
| Group | Hurt below | Examples |
|---|---|---|
| Houseplants, tropicals | 45–50 °F | Most houseplants come from the tropics. Depending on the plant, damage starts below 45 to 50 °F (University of Minnesota), and nearly all die below freezing, so bring them in when nights dip to about 50 °F (Iowa State). |
| Tender | 32 °F | Basil and bush beans: a light frost of 30 to 32 °F kills them (University of Minnesota). Purdue also lists tomatoes and sweet corn as damaged by frost, and peppers, squash, cucumbers and melons as very tender. |
| Half-hardy | about 28 °F | Broccoli, cauliflower, lettuce, spinach, chard and turnips survive a light frost; beets, peas and green onions the high 20s (University of Minnesota). Sweet alyssum and snapdragons often come through 28 °F, sometimes 26 °F (Iowa State). |
| Hardy | about 20 °F | Kale, collards, cabbage and Brussels sprouts, the hardiest (University of Minnesota). |
Flowers can surprise you. After a 31 °F night, Iowa State photographed a container where the petunia stayed green and the coleus next to it was killed.
What doesn’t need covering: perennials, shrubs, roses and trees. In fall they need the cold to go dormant, and most take temperatures at or just below freezing with little damage (Iowa State). In spring, the new shoots of tulips, daffodils and most perennials take the low 30s and upper 20s °F. Blossoms on fruit trees can be hurt, but covering a tree isn’t practical.
How to cover plants for frost
- Watch the forecast. Once the overnight lows dip to the mid-30s °F, it’s time to act (Iowa State). Clear, calm nights are the risky ones (University of Arizona): clouds hold the ground’s heat in, so frost is less likely on cloudy nights (Penn State).
- Water dry soil a few days ahead. Moist soil stores more of the day’s heat and gives it back at night (Penn State). UC IPM waters dry topsoil at least 3 days before the cold; UC Master Gardeners in Solano County water 2 to 3 days before, not right before, and never water succulents before a frost.
- Cover before sunset. UC Master Gardeners put the covers on right before sunset. The cover traps the warmth rising from the ground, which keeps frost off the leaves (Iowa State).
- Hold it off the leaves. Prop the cover on stakes, wire loops, tomato cages or patio furniture (Iowa State, UC Master Gardeners). Where row cover touches the leaves, frost can still form on them (Clemson).
- Let it reach the ground. Drape the cover all the way down, but don’t gather it around the stem or trunk: the warmth comes up from the soil (UC IPM, University of Arizona).
- Uncover in the morning. Take the cover off the next day once it’s above freezing (Iowa State). The University of Arizona removes sheets and blankets when it warms to about 50 °F under them; frost cloth can stay on longer.
What to cover plants with
| Cover | Use it? | Notes |
|---|---|---|
| Frost cloth, row cover | Yes, the best | The University of Arizona calls sheets and blankets minimal protection and uses frost cloth for more: some protect to 20 °F, and many can be left on for long stretches. Light row cover (0.5 to 1 oz) is for frost down to 28 °F, heavier cloth for colder snaps (Clemson). |
| Old sheets, blankets, towels | Yes | On Iowa State’s list of covers. Take them off in the morning. |
| Cardboard box | Yes, for small plants | UC Master Gardeners list boxes with sheets, burlap and frost cloth. |
| Upside-down pot | Yes, for small plants | Clemson covers perennials that come up too early with black plastic nursery pots when frost is forecast. |
| Plastic sheet, garbage bag | Only off the leaves | UC IPM and the University of Arizona use cloth or paper, not plastic. If plastic is all you have, keep it off the plant and take it off first thing: plants can scorch in the sun under it (Clemson). |
| Pine straw | For pansy beds | UGA spreads 2 to 4 inches over pansies, plants and all, in hard cold and rakes it off afterward. |
What to bring indoors
- Houseplants that summered outside. Bring them in when nights dip consistently to about 50 °F, well before they get near freezing, and check them for pests first (Iowa State).
- Pots of annuals and tropical plants. Moving them into a garage, a porch or a heated room for the night is the easiest protection there is (Iowa State). Pots that stay out are colder at the roots than plants in the ground: on some otherwise hardy plants, root damage can begin at 28 °F, so Clemson packs pots close together with mulch or soil around them.
- Holiday cacti. A Christmas cactus can summer outdoors but comes in before frost; Christmas cactus care has the bring-in date for your ZIP code.
- Dahlias and other tender bulbs. Leave them until frost blackens the leaves, then dig and store them: see how to store dahlia tubers.
Save your ZIP code in My garden to keep your frost dates and fall jobs in one place.
After a frost
- Wait before you prune. Frozen leaves and shoots look water-soaked and wilted, then turn black within hours or days (Clemson). Don’t cut anything back until you can tell what’s dead, ideally when new growth starts in spring (UC IPM). The University of Arizona notes that damaged leaves help trap warm air around the plant, and that new growth often comes from stems that looked dead.
- Pull frost-killed annuals. Tender vegetables like tomatoes and beans don’t come back once frost kills them. Texas A&M groups them together in fall gardens so they can be pulled out after the first killing frost.
Questions people ask
What temperature is frost for plants?
Leaves frost at 32 °F, but they cool below the air on clear nights, so frost can form while the air is still 33 to 36 °F (National Weather Service). A light frost of 30 to 32 °F kills tender plants (University of Minnesota).
What temperature should I cover my plants?
Cover tender plants when the forecast low reaches the mid-30s °F (Iowa State). Half-hardy plants take a light frost; when 28 °F or colder is forecast, give them frost cloth, since sheets stop helping below about 28 °F (Iowa State) and heavier cloth protects to colder temperatures (Clemson).
Will one night of frost kill my plants?
It will kill tender ones: a light frost of 30 to 32 °F kills bush beans (University of Minnesota). Half-hardy and hardy plants come through a light frost, and so do perennials and spring bulbs (Iowa State). How long it lasts matters: Iowa State sees damage above 28 °F when it stays below freezing for 5 hours or more.
Can I use garbage bags to cover plants?
Cloth is better: UC IPM and the University of Arizona say cloth or paper, not plastic. If a bag is all you have, hold it off the leaves on stakes, let it reach the ground and take it off first thing in the morning; Clemson warns that plants under plastic can scorch in the sun.
Will cardboard boxes protect plants from frost?
Yes, for small plants. UC Master Gardeners list cardboard boxes with sheets and frost cloth. Set the box over the plant before sunset and lift it off the next morning.
When should I take frost covers off?
The next morning, once the air is above freezing (Iowa State). The University of Arizona takes sheets and blankets off when it warms to about 50 °F under them, so the plants don’t overheat; frost cloth can stay on longer.
Can mums survive frost?
Hardy garden mums can: the University of Minnesota’s Mammoth mums keep blooming well into October thanks to their frost tolerance. The flowers and buds are the tender part. Florist mums bloom late, and freezing temperatures often kill their buds before they open (Iowa State), so move potted mums into a garage or cover them on a freezing night. After a hard frost, Illinois Extension keeps potted mums that won’t be planted in a cool, dark spot for the winter.
Can pansies survive frost?
Yes. Pansies tolerate light freezes very well (Iowa State), and healthy plants survive short spells down to the single digits (UGA Extension). Below 25 °F their leaves wilt and turn gray-green, a normal defense. UGA covers pansy beds with 2 to 4 inches of pine straw only for forecasts below 20 °F lasting several hours, with drying winds and a risk of the soil freezing.
Can tomato plants survive frost?
No. Tomatoes are tender: Purdue Extension lists them as damaged by frost, and a light freeze of 29 to 32 °F kills tender plants (National Weather Service). Cover them when the forecast low reaches the mid-30s.
How do I protect potted plants from frost?
Move them into a garage, a porch or a heated room for the night (Iowa State). Roots in a pot get colder than roots in the ground; Clemson packs pots that stay out close together, with mulch or soil around them.
Sources
- Iowa State University Extension and Outreach, How to Protect Plants from Frost and Freeze (Aaron Steil; reviewed October 2026): frost and freeze; NWS frost advisories at 33–36 °F; act when lows dip to the mid-30s; bringing plants in; sheets, blankets, towels, tarps, frost fabric and row cover trap radiant heat from the ground; covers stop working below about 28 °F, and damage above 28 °F after 5 hours or more below freezing; covers held off the foliage and removed the next day above freezing; perennials and woody plants need no protection; spring bulbs and perennials take the low 30s and upper 20s; cool-season vegetables and annuals often to 28 °F, sometimes 26 °F; the petunia and coleus at 31 °F. Also How and when do I bring my houseplants back indoors? (updated October 1, 2026): about 50 °F nights; damage in the mid-to-lower 40s. Growing Chrysanthemums in Iowa (Aaron Steil; reviewed September 2025): freezing temperatures destroy florist mums’ buds. Growing Pansies & Violas (Aaron Steil; reviewed March 2025): pansies tolerate light freezes very well.
- University of Minnesota Extension, Planting vegetables in midsummer for fall harvest (Jill MacKenzie; reviewed 2026): a light frost of 30–32 °F kills bush beans; cold hardiness by crop, from killed by frost to the hardiest, down to 20 °F. When to bring houseplants inside for the winter: damage below 45–50 °F, depending on the species. Hardy mums provide color that returns every fall (Robin Trott, August 25, 2026): frost tolerance keeps the Mammoth mums blooming into October.
- National Weather Service, Glossary: frost, frost advisory, freeze and hard freeze (28 °F or lower for an extended time, killing most vegetation); NWS Raleigh, Frost/Freeze Information: frost advisories for 33–36 °F with good radiation conditions, frost possible below 36 °F; NWS Midland/Odessa, Midland freeze data: light (29–32 °F), moderate (25–28 °F) and severe (24 °F and below) freezes.
- UC Statewide IPM Program, Freezing and Frost: frost and freezing; water dry topsoil at least 3 days before the cold; cover overnight with cloth, not plastic, open at the bottom; remove covers by day; wait to prune. UC Master Gardeners of Solano County, Do’s and Don’ts When Preparing for Frost (November 30, 2022): water 2–3 days before; cover right before sunset with sheets, burlap, frost cloth or cardboard boxes; uncover the next morning; don’t water succulents.
- University of Arizona Cooperative Extension, Frost Protection (AZ1002, Lucy Bradley, 1998): calm, clear nights; cloth or paper, not plastic; frost cloth to 30 °F, some to 20 °F; drape to the ground, not gathered at the trunk; sheets off at about 50 °F under the cover; damaged leaves shelter the plant; wait for new growth to prune.
- Clemson Cooperative Extension, Home & Garden Information Center: Extending the Growing Season in South Carolina (Julia Nichols, November 20, 2025): row cover held off the leaves; 0.5–1 oz cover for frost down to 28 °F. Cold Damage: root damage from 28 °F on some hardy plants in containers; pots packed together and mulched; black nursery pots over early perennials; frozen tissue water-soaked, then black. Winter Damage (January 7, 2019): plastic off the plants, or removed the next day, as plants can scorch in the sun.
- Penn State Extension, Frost, Critical Temperatures, and Frost Protection (Rob Crassweller; updated March 18, 2024): radiation frosts on clear, calm nights; fewer under clouds; moist soil stores more heat.
- UGA Extension, Success with Pansies in the Winter Landscape (Bulletin 1359, Bodie V. Pennisi; full review November 16, 2023): pansies survive the single digits; foliage wilts below 25 °F; pine straw 2–4 in when below 20 °F is forecast for several hours.
- University of Illinois Extension, Why do my mums always die? (Ken Johnson, September 10, 2021): potted mums to a cool, dark spot after a hard frost.
- Purdue Extension, Indiana Vegetable Planting Calendar (HO-186-W, Rosie Lerner, 2020): tomatoes, beans and sweet corn tender, damaged by frost; peppers, squash, cucumbers and melons very tender. Texas A&M AgriLife Extension, Fall Vegetable Gardening Guide for Texas (Larry Stein and Joe Masabni): frost-susceptible crops planted together, to be removed after a killing frost.
- Frost dates in the checker: NOAA National Centers for Environmental Information, U.S. Climate Normals 1991–2020, 32 °F and 28 °F freeze dates by station; ZIP code centers from the U.S. Census Bureau’s 2024 Gazetteer files.