Frost will kill tomato plants, but you can save them with covers, water, or by moving them indoors

Tomato plants die when frost forms on their leaves and stems — the ice crystals rupture the plant's cells, and the damage is usually permanent. A hard frost (below 28°F) kills most tomatoes outright. A light frost (28°F to 32°F) may damage leaves and slow growth, but the plant can recover if you protect it quickly. The key is acting before the frost arrives: once ice forms, it is too late.

Your protection method depends on how much warning you have, how cold it will get, and whether your plants are in the ground or in containers. A frost cloth draped over plants works for light frosts. Watering the soil before a frost can help. Moving potted plants indoors is the most reliable method if you have the space. Knowing which method fits your situation means your tomatoes survive the cold snap and keep producing.

Key Takeaways

  • Frost cloth or old sheets draped directly over plants trap warmth and work best for light frosts above 28°F.
  • Watering the soil thoroughly the day before a frost helps the ground release heat overnight, protecting roots and lower stems.
  • Potted tomatoes should be moved indoors to a garage, basement, or unheated room before the frost arrives.
  • Remove covers or bring plants back outside during the day once temperatures rise above 50°F, or the plants will overheat and weaken.
  • Hardening off seedlings by exposing them gradually to cold air in spring makes them more frost-resistant later in the season.

Using frost cloth and covers to trap heat

Frost cloth is a lightweight, breathable fabric sold at garden centers and online — it looks like thin white or tan fabric and comes in rolls. Drape it directly over the tomato plant, letting it touch the leaves and stem, and anchor it to the ground with soil, rocks, or stakes so wind does not blow it away. The cloth traps the plant's own heat and slows heat loss to the air above. It works best for light frosts (28°F to 32°F) and will not protect plants in a hard freeze.

If you do not have frost cloth, old bed sheets, blankets, or burlap work in a pinch — anything that creates a barrier between the plant and the cold air. Avoid plastic sheeting: it conducts cold and can damage leaves if it touches them directly. Leave the cover on until the temperature rises above 50°F the next morning, then remove it so the plant does not overheat. If another frost is forecast for the following night, you can cover the plant again.

Watering soil before a frost to release ground heat

Wet soil holds heat better than dry soil and releases that heat slowly overnight. Water the base of each tomato plant thoroughly the afternoon before a frost is forecast — soak the soil so it is wet 6 to 8 inches deep. The water absorbs the sun's warmth during the day, and as the air temperature drops at night, the soil releases that stored heat upward, warming the plant's roots and lower stem.

This method works best when combined with a cover, but it also helps on its own during a light frost. It will not protect plants in a hard freeze, and it does not replace frost cloth or moving plants indoors. Water only the soil, not the leaves — wet foliage actually freezes faster and can increase frost damage. If the forecast calls for temperatures below 28°F, watering alone is not enough; use a cover or move the plant indoors.

Moving potted tomatoes indoors before frost

If your tomatoes are in containers, moving them indoors is the most reliable protection. Bring them inside to a garage, basement, unheated shed, or any room that stays above freezing — it does not need to be warm, just frost-free. Do this the afternoon before the frost arrives, not after the temperature has already dropped. A potted plant brought in after frost has formed will not recover.

Place the pots in a location with some light if possible — a basement window or garage with a door window is ideal. The plants will slow their growth in the cold and dim light, but they will survive. Once the outdoor temperature stays above 50°F during the day and does not drop below 40°F at night, move the pots back outside. Harden them off by leaving them outside for a few hours the first day, then gradually increasing the time over three to five days, so the leaves do not sunburn.

Hardening off seedlings in spring to build frost tolerance

Seedlings started indoors are tender and will not survive even a light frost if you plant them directly in the garden. Harden them off by exposing them gradually to outdoor conditions over seven to ten days before planting. Start by setting the seedlings outside in a sheltered, shaded spot for one to two hours on the first day. Each day, increase the time outdoors and move them into more direct sun, until they spend a full day and night outside.

Hardened-off seedlings develop thicker leaves and stronger stems and are much more frost-resistant than plants moved straight from a warm indoor shelf to the garden. Even hardened seedlings will not survive a hard frost, but they can handle a light frost better than tender seedlings. Harden off all transplants, whether you grew them yourself or bought them from a nursery.

Timing: when to cover and when to uncover

Cover plants in the late afternoon, before the sun sets — do not wait until dark. This gives the cover time to settle and trap the warmth still radiating from the soil. Check the weather forecast the evening before the frost is predicted; if the forecast changes and frost is no longer expected, you do not need to cover. If frost does arrive, leave the cover on until the temperature rises above 50°F the next morning.

Remove covers during the day even if it is still cool outside. Plants under covers in daylight will overheat, sweat, and weaken. If the forecast calls for frost again that night, you can cover them again the following afternoon. If frost is predicted for several nights in a row, cover and uncover each day — it is tedious, but it keeps the plants alive and growing.

What to do if frost damage has already occurred

If frost has already damaged your tomato plant, do not prune the damaged leaves when ready. Wait three to five days to see how much damage is permanent. Leaves that are blackened or mushy are dead, but leaves that are just wilted may recover. Once you can see which parts are truly dead, remove only those sections with clean pruning shears.

A plant that has been frosted will slow its growth and may drop some flowers or small fruit, but it usually recovers and keeps producing if the main stem is still alive. If the entire plant is blackened and mushy from a hard freeze, it is dead and should be removed. In that case, you can plant a new tomato seedling if there is still time before the first fall frost in your area.

Frequently Asked Questions

Can I use plastic sheeting to cover tomato plants?

Plastic conducts cold and does not trap heat the way cloth does. If plastic touches the plant's leaves, it can actually increase frost damage. Use frost cloth, old sheets, or blankets instead. Plastic is fine as a windbreak around the cover, but the layer touching the plant should be fabric.

How cold does it have to be before tomatoes die?

A hard frost at 28°F or below will kill most tomato plants outright. A light frost between 28°F and 32°F damages leaves and slows growth but usually does not kill the plant if you cover it. Temperatures above 32°F do not cause frost damage, though the plant may slow growth.

Should I water my tomatoes if frost is coming?

Yes, water the soil thoroughly the afternoon before a frost is forecast. Wet soil releases heat overnight and protects the roots and lower stem. Water only the soil, not the leaves, because wet foliage freezes faster and increases damage.

What if I cover my tomatoes but they still freeze?

If the temperature drops below 28°F, a cover alone may not be enough. Combine a cover with watering the soil, or move potted plants indoors. For in-ground plants in a hard freeze, there is no reliable protection other than moving them, which is not practical for large plants.

Can I leave frost cloth on my tomatoes all day?

No. Remove the cover once the temperature rises above 50°F in the morning. Leaving it on during the day traps heat and causes the plant to overheat and weaken. You can put it back on the following afternoon if another frost is forecast.