How do I protect tomato plants from frost?

Drape frost cloth over the plants on the nights your yard drops to freezing, and weight the edges to the soil so it traps the heat rising from the ground. Put the cover on before sunset, while the ground is still warm. Cover only the nights the adjusted low reaches near freezing, and leave the plants open through warmer spells.

At what temperature should I cover tomatoes?

Cover when the overnight low adjusted for your yard reaches about 34°F. When the night is calm and the sky is clear, a leaf sheds heat upward and can drop a couple of degrees below the surrounding air. Ice can then form on the plant while the thermometer reads a little above freezing.

Can tomato plants survive one night of frost?

A hard freeze kills a tomato plant outright, and even a light radiative frost can blacken the top growth and leave it as mush by afternoon. Tomato tissue is mostly water, and when that water freezes the ice ruptures the cells. One unprotected freezing night usually ends the plant.

Should I cover tomatoes every night in fall?

No. Cover only on the nights the adjusted low for your yard reaches near freezing. Warm nights carry no risk, and a cover left on through a mild spell traps heat and slows the plant. Watch the forecast low, correct it for how cold your beds run, and act on the nights that cross the line.

August 5, 2026 · Updated September 12, 2026

How to protect tomato plants from frost

Cover your tomatoes on the first night your yard drops to freezing, and no earlier. A tomato is a tropical plant. When ice forms inside its leaf cells, the cell walls rupture and the plant blackens within a day. The forecast low for your area often runs warmer than the low in your beds, so the freeze can arrive before the regional number says it will.

Why a light frost kills a tomato outright

Once the sun goes down, the ground begins shedding the warmth it built up through the day, and that heat rises toward the open sky. When the night is calm and cloudless, a leaf loses heat faster than the surrounding air does. That leaf can settle a few degrees colder than the thermometer beside it. Tomato tissue is mostly water. Once that water freezes, ice crystals tear the cells, and the leaf collapses. A hard freeze takes the whole plant. A light radiative frost can kill the top growth and leave you with mush by the next afternoon. We cover the temperature thresholds in the tomato frost-kill guide.

Why your yard freezes before the forecast

Chilled air is heavier than warm air. On a calm night it slides downhill and collects in the lowest parts of your yard. The regional forecast is modeled for a wide area, and it cannot see the dip your beds sit in or the way your fence blocks the breeze that would otherwise mix the air. That gap is measurable. In our own garden the station reads 7\u00b0F colder than the forecast on these nights. The published first fall frost for our area lands on October 22, but corrected for our site it falls on September 30, and we recorded our first fall frost on October 3.

This is why the printed frost date misleads so many gardeners. It is a regional average, and your yard has its own low. We walk through that gap in why your frost date is probably wrong.

You can find your own offset two ways. A free Siltwell account lets you enter a manual offset in Settings once you know how much colder your yard runs. A connected station on Pro learns the offset for you by comparing its readings to the forecast, and it trusts the number only after about 14 overlapping days of data. If you have no station yet, the public microclimate checker measures how much colder nearby home stations ran than the forecast on recent nights, and estimates the offset for your area.

The checker reports how many nearby stations it read and how far to trust the estimate for your area. It cannot promise the exact low in your one yard, because your dip and your fence are yours alone. Treat it as a starting correction, then refine it once you have measured a few frost nights of your own.

What temperature to cover at, and how

Cover when the adjusted low for your yard reaches about 34\u00b0F. Use the corrected number, since the raw forecast usually reads warmer than your beds. The leaf can sit below the air on a clear, still night, so a couple of degrees of margin protects the plant. On a windy or cloudy night the leaf and the air stay closer together, and the risk drops. Frost cloth works by trapping the heat radiating up from the soil, so it buys you a margin over the open sky. The exact degrees depend on the fabric and the night, which we cover in the frost blanket guide.

Drape the cover all the way to the soil and weight the edges. The warmth comes from the ground. The plant itself gives off almost none. A cover that stops at the stems lets the heat escape and does almost nothing.

Should you cover every night in fall

You do not need to cover every night. Tomatoes take no frost damage on a night that stays in the 40s, so covering then only slows the plant and wastes your evenings. Watch the forecast low, correct it by your yard's offset, and act on the nights that cross near freezing. In our garden we transplanted tomatoes into a raised bed in mid-May and kept picking fruit into early September, so a single well-timed cover late in the season can add weeks of harvest.

Set your threshold now, before the first cold snap catches you. Decide the adjusted low that sends you out with the cloth, keep the fabric where you can reach it after dark, and check the corrected low each evening once the nights turn. If your yard freezes on a night the forecast calls 36\u00b0F, you will already know to cover.

Common questions

How do I protect tomato plants from frost?: Drape frost cloth over the plants on the nights your yard drops to freezing, and weight the edges to the soil so it traps the heat rising from the ground. Put the cover on before sunset, while the ground is still warm. Cover only the nights the adjusted low reaches near freezing, and leave the plants open through warmer spells.
At what temperature should I cover tomatoes?: Cover when the overnight low adjusted for your yard reaches about 34°F. When the night is calm and the sky is clear, a leaf sheds heat upward and can drop a couple of degrees below the surrounding air. Ice can then form on the plant while the thermometer reads a little above freezing.
Can tomato plants survive one night of frost?: A hard freeze kills a tomato plant outright, and even a light radiative frost can blacken the top growth and leave it as mush by afternoon. Tomato tissue is mostly water, and when that water freezes the ice ruptures the cells. One unprotected freezing night usually ends the plant.
Should I cover tomatoes every night in fall?: No. Cover only on the nights the adjusted low for your yard reaches near freezing. Warm nights carry no risk, and a cover left on through a mild spell traps heat and slows the plant. Watch the forecast low, correct it for how cold your beds run, and act on the nights that cross the line.

Related guides

Free planting tools

When to plant — the last date to sow each crop before your fall frost
Microclimate checker — how much colder your yard runs than the forecast
GDD estimator — whether a crop will ripen where you are