How to Protect Plants From Frost and a Hard Freeze

Updated September 2026 · Garden Advice Guide

Knowing how to protect plants from frost comes down to one idea: keep the heat the soil soaked up during the day from escaping into the night sky, and keep it around the plant instead. A cover that reaches the ground does that best, a good soak of water the afternoon before helps the soil store more heat, and pots simply come inside. Frost (33 to 36°F on the thermometer, colder on the leaf) mostly hurts tender annuals and vegetables. A freeze (32°F) kills them outright. A hard freeze (28°F and below for a few hours) reaches into things you thought were safe, and no bedsheet saves a basil plant at 25°F.

Find your date first: look up your average first fall frost with our free frost date lookup so you know roughly which week to start watching the overnight forecast instead of getting caught by it.

Updated September 2026

Frost vs freeze vs hard freeze: the temperatures that matter

People use "frost" and "freeze" as if they're the same thing, and the difference decides which of your plants survive the night. Here's how the National Weather Service splits them, and what each one does in a garden.

Two things in that table catch people out.

First, the frost line. A forecast low of 35°F can still leave your squash leaves black in the morning. On a clear, still night the leaf surface loses heat faster than the air, so it reaches 32°F while your porch thermometer reads three or four degrees warmer. That's why "frost advisory" nights get treated as a freeze in this article.

Second, the hard freeze line at 28°F is where most of the easy tricks stop working. Between 29 and 36°F, a cover, a soak, or a move under the eaves buys you a plant. Below 28°F, you need a heavier cover with a heat source, or you accept the loss and harvest what you can the afternoon before.

How to read the forecast for your own yard

Your yard isn't the airport where the forecast is measured. Cold air sinks, so a low spot, the bottom of a slope, or an open lawn away from the house frosts first. Beds against a south wall, under a tree canopy, or next to pavement stay warmer, sometimes by 4 or 5 degrees.

The signs that a forecast low will overshoot in your yard:

• Clear sky. Clouds act as a blanket. A clear night radiates heat away fast.
• Calm air, under 5 mph. Wind mixes warmer air down from above. Still air lets the cold pool.
• Low dew point. If the dew point is in the low 20s, there's little moisture to slow the temperature drop. Take the forecast low and subtract 2 or 3 degrees.
• A low spot. Your bed at the bottom of the yard can run 5 degrees colder than the top.

If two or more of those are true, treat a forecast of 36°F as a freeze.

How to protect plants from frost: the full toolkit, ranked

Here's every method that works, in the order you should reach for them. The first three handle almost every frost night of the year.

1. Cover them (the one that works every time)

A cover traps the heat radiating out of the soil and holds it in a pocket of air around the plant. That's the whole trick, and it's why a cover has to reach the ground on all sides. A cover draped over the top of a plant and tied around the stem is a scarf, not a blanket. The heat escapes underneath and the plant freezes anyway.

What to use, best to worst:

Purpose-made frost cloth beats everything else because it breathes, so you can leave it on through a run of cold nights without cooking or smothering the plants. The weights, the hoops-versus-draping choice, and the exact timing all have their own page: frost cloth for plants. This page stays on the wider method set.

Whatever you use, get it on in the late afternoon while the soil is still warm, and pull it back once the air is above freezing the next morning (sheets and plastic especially). Weigh the edges down with bricks, boards, or soil so wind can't lift them.

2. Water the soil the afternoon before

Wet soil holds far more heat than dry soil, and it releases that heat slowly through the night. Watering thoroughly by early afternoon on a frost day can keep the air around low plants a degree or two warmer than a dry bed, and it puts your plants into the cold fully hydrated, which matters because frost damage is partly a drying injury.

Water the soil, not the leaves. Wet foliage going into a freeze is a liability. Aim for a deep soak that reaches 6 inches down. Our watering guide gives the inches per week your beds need at this time of year if you want to be precise about it.

Watering helps most with a light frost (33 to 36°F) on plants close to the ground. It won't save tomatoes at 28°F on its own. It's a partner to a cover, not a replacement.

3. Bring pots and hanging baskets inside

Roots in a pot have no ground warmth to draw on, so containers freeze faster and harder than the same plant in a bed. A 10-gallon pot on a patio can be 5 to 10 degrees colder at the root zone than soil in the ground.

The good news is they move. Options in order of effort:

• Into the garage, shed, or an unheated porch. Even an unheated enclosed space stays above freezing on a frost night. This is where most people's pots should go.
• Against the house under the eaves, on the south or east side. The wall radiates heat all night and the roof blocks the sky. Usually good for 3 to 5°F.
• Grouped tightly together on the patio with a sheet thrown over the group. The mass of soil helps, and one sheet covers six pots.
• Indoors for houseplants that summered outside. They should come in when nights hit the 50s anyway, well before frost.

If you've got a fall container display going, our page on fall flowers for pots sorts which of them can stay out through a frost and which need to move. Pansies and ornamental kale stay. Coleus and sweet potato vine don't.

4. Mulch, but only for the roots

Mulch is a root protector, not a frost cover. A 2 to 3 inch layer of straw, shredded leaves, or bark over the root zone keeps the soil from freezing and thawing repeatedly, which is what heaves perennials out of the ground and kills strawberries and garlic over winter.

But on a single frost night, deep mulch under a plant works against you. It insulates the warm soil away from the leaves above it. So the rule is:

• Frost night, tender plant you're covering: leave the soil bare or lightly mulched under the cover so its heat can rise.
• Winter protection for roots and crowns: mulch after the ground has frozen or is close to it, not before.

Our mulch guide covers depths and materials, and the page on when to cover strawberries is the worked version of the "after the ground freezes" rule.

5. Harvest ahead of it

For vegetables, the best frost protection is sometimes a basket. Pick every tomato that has started to blush, every pepper, all the basil, the last summer squash, and any beans. Green tomatoes ripen indoors on the counter. Our when to harvest tool tells you what's ready and what can wait, crop by crop.

Then leave what enjoys the cold. Kale, collards, Brussels sprouts, carrots, parsnips, and leeks all get sweeter after a frost. Lettuce and spinach take a light frost but want a cover for a hard freeze.

6. Sprinklers running through the night (the commercial trick, with a catch)

Citrus and strawberry growers run sprinklers all night during a freeze. As water freezes on the plant it releases heat, and a continuous ice coat holds the leaf right at 32°F. It works, and it protects to the low 20s.

The catch is "continuous." The sprinkler has to run from before the temperature hits 32°F until the ice melts off in the morning, without a break. If it stops, the evaporating water pulls heat out of the plant and you get worse damage than doing nothing. Ice weight also snaps branches. For a home garden it's a lot of water and risk for a small bed. Cover instead.

7. Heat under the cover for a hard freeze

Below 28°F, a cover alone runs out. The fix is a heat source inside the tent: a string of old-style incandescent Christmas lights (the C7 or C9 bulbs that get warm, not LEDs), or a few gallon jugs of hot water set under the cloth at dusk. A dozen incandescent bulbs under a heavy frost cloth can hold a small bed several degrees above the outside air. This is how people keep peppers producing into November.

Which plants can take what

This is the part most guides skip. The right method depends on the plant, and half your garden doesn't need protecting at all.

Exact tolerance varies by cultivar and by how hardened the plant is. A pansy that's been outside through a week of cool nights shrugs off the low 20s. The same pansy straight out of a warm greenhouse can brown at 26°F. If a plant just came home from the store, treat it as one group more tender than the table says for its first week. The same logic runs in reverse in spring, which is what hardening off seedlings is for.

For perennials, know your zone. A plant rated to your USDA hardiness zone or colder doesn't need any fall frost protection; it's built for far worse in January.

The morning after: what to do with frosted plants

Don't rush out at 7 a.m. and start cutting. Frosted plants often look worse than they are, and cutting cold, wet tissue spreads the damage.

1. Wait for the thaw. Let the sun do its work. Leaves that were merely frosted often perk back up by noon.
2. Then take covers off. Sheets and plastic come off once the air is above freezing. Frost cloth can stay if more cold is coming.
3. Sort the damage. Blackened, water-soaked, limp leaves are dead. Wilted but still green leaves may recover.
4. Leave dead tissue on for a few days if more frost is coming. It shields what's under it.
5. Cut back only once the weather settles. On perennials, wait until the top growth is fully brown, then cut. On tender annuals that got hit hard, pull them and put the healthy remains in the compost.
6. Don't fertilize. A frost-stressed plant pushed into soft new growth is set up to be killed by the next one.
7. Water if the soil is dry. Frost injury is partly dehydration.

For what to pull and what to leave standing for the winter, our fall garden cleanup page runs through the sorting decisions bed by bed.

Worked example: a zone 6a garden on October 6

You're in zone 6a, where our lookup puts the average first fall frost around October 5 to 8. Tonight's forecast: low of 34°F, clear, wind calm, dew point 26°F. Three of the four warning signs are lit, so you treat this as a freeze night with a real low around 31°F in the open beds and colder in the low spot by the fence.

Here's the afternoon plan, in order, and it takes under an hour.

• 2 p.m. Deep-water the vegetable bed and the flower border. Skip the leaves.
• 3 p.m. Harvest: every tomato showing color, all the peppers, the last of the basil, two zucchini. Green tomatoes go in a paper bag on the counter.
• 3:30 p.m. Drape medium-weight frost cloth over the pepper row (you want them producing another two weeks) and the lettuce. Edges pinned to the soil with bricks.
• 4 p.m. Move the coleus, the sweet potato vine basket, and the ornamental pepper into the garage. The pansies, mums, and kale in pots stay out. They'll be fine to well below tonight's low.
• 4:15 p.m. Old bedsheet over the dahlias, weighted with a couple of boards, because you want two more weeks of flowers before you dig the tubers.
• Leave alone: the kale, carrots, chard, parsley, and the whole perennial border. The chard is half-hardy but 31°F won't hurt it. The rest want the cold.

Next morning the thermometer bottomed at 30°F. The uncovered marigolds are done. The dahlias under the sheet are fine, the peppers under the cloth are fine, the kale looks better than yesterday. Sheet comes off at 9 a.m. once the air reads 35°F. The frost cloth stays on because the forecast shows two more cold nights, then a warm week. That warm week is when the peppers finish, and the cloth comes off for good on the 12th.

Spring frost: the same rules in reverse

Everything above applies to the spring side of the season, with one change of emphasis. In fall you're protecting mature plants for a few extra weeks of harvest. In spring you're protecting seedlings that have no reserves, and a single frost can end them.

The spring rules:

• Don't set out tender plants until a week or two past your average last frost. The planting calendar counts the weeks off your date for you.
• Keep a sheet or cloth by the door until late May in zones 5 and 6, mid-May in zone 7.
• Fruit trees in bloom are the biggest spring loss. Open blossoms die at about 28°F. Cover small trees; you can't cover big ones, so pick sheltered planting spots to begin with. Figs are the classic borderline case here, and our page on the fig tree growing zone covers wrapping and mulching a marginal one.
• Frost on the lawn is harmless. Just stay off it until it thaws, since walking on frozen grass blades breaks them.

Frequently asked questions

At what temperature should I cover my plants?

Cover tender plants (tomatoes, peppers, basil, coleus, impatiens) whenever the forecast low is 36°F or below, since the leaf surface gets colder than the air. Cover half-hardy plants like snapdragons, petunias, and lettuce at 30°F and below. Hardy plants such as pansies, kale, and most perennials don't need covering at all in fall.

Does watering plants before a frost really help?

Yes, within limits. Moist soil stores and releases more heat overnight than dry soil, which can keep low-growing plants a degree or two warmer, and a fully hydrated plant handles the cold better. Water the soil by early afternoon, keep the leaves dry, and treat it as a partner to a cover rather than a replacement for one.

Can plants recover from frost damage?

Often, yes. Leaves that wilt but stay green usually recover by midday. Leaves that turn black and water-soaked are dead, but the plant may push new growth from lower buds if the stem and roots weren't frozen. Wait a few days before cutting anything so you can see where the live tissue ends, and never fertilize a frost-damaged plant.

What is the difference between a frost and a freeze?

A frost happens when the air is between 33 and 36°F but leaf surfaces radiate enough heat to drop below 32°F and form ice crystals. A freeze is when the air itself reaches 32°F or lower. A hard freeze is 28°F and below for a few hours. Frost damages tender plants, a freeze kills them, and a hard freeze reaches half-hardy plants that survived the first frost.

Should I bring my potted plants inside for a frost?

Tender plants in pots, yes, every time. Container roots have no ground warmth and freeze faster than the same plant in a bed. An unheated garage, shed, or enclosed porch is enough for a frost night. Hardy container plants like pansies, violas, ornamental kale, heuchera, and mums can stay outside through frosts and light freezes.

Will a bedsheet protect plants from frost?

A sheet buys about 2 to 4 degrees, which is enough for a light frost of 33 to 36°F but not for a hard freeze. It has to reach the ground on all sides and be weighed down, and it needs to come off the next morning because it soaks up moisture and blocks light. For anything below 30°F, or a run of cold nights, use frost cloth instead.

How do I protect vegetables from frost without covering them?

Harvest what's ripe or nearly ripe, water the bed deeply in the afternoon, and leave the cold-tolerant crops alone. Kale, collards, carrots, parsnips, Brussels sprouts, spinach, and leeks all improve after frost. Peppers, tomatoes, beans, cucumbers, and squash are the ones that need a cover or a basket, and there's no third option for them once the air hits 32°F.

Is frost on the lawn a problem?

No. Grass blades freeze and thaw without harm. The only rule is to stay off a frosted lawn until it thaws, because frozen blades snap under foot traffic and leave brown footprints that last for weeks.