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

Tomatoes die when the temperature drops to 32°F (0°C) or below. Frost — the ice crystals that form on plants overnight — damages the cells in leaves and stems, turning them black and mushy within hours. If frost is forecast and your tomatoes are still in the ground or in containers, you have a narrow window to act: usually the evening before the frost arrives through early morning when temperatures are still dropping.

The method you choose depends on how many plants you have, whether they are in the ground or containers, and how much time you have. A single potted plant can move indoors. A row of garden tomatoes needs a cover or heat source. A large planting may not be worth saving if the season is nearly over.

Key Takeaways

  • Frost damage happens at 32°F and below, and tomato plants cannot recover from it — prevention is your only option.
  • Row covers, blankets, or plastic sheeting draped over plants and anchored to the ground will trap heat and raise the temperature by 2 to 8 degrees.
  • Watering the soil deeply the day before frost arrives helps the ground hold heat overnight and release it slowly.
  • Potted tomatoes can be moved into a garage, shed, or indoors if temperatures will stay above freezing inside.
  • Frost cloth or burlap works better than plastic for repeated use, because plastic can touch leaves and cause damage where it makes contact.

Using row covers and blankets to trap heat

A row cover is a lightweight fabric you drape over plants to trap warm air. It lets light and water through but creates a barrier that raises the temperature underneath by 2 to 8 degrees Fahrenheit, depending on the fabric weight and how well you seal the edges. Frost cloth, available at garden centers, is designed for this and can be reused for years. Bed sheets, old blankets, or burlap work in a pinch, though they are heavier and can damage branches if they sag.

Install the cover in the late afternoon, before temperatures start dropping. Drape it loosely over the plant so it does not touch the leaves — frost damage can occur where the fabric makes contact with cold foliage. Anchor the edges to the ground with soil, rocks, or stakes so wind does not lift it and cold air does not seep underneath. Leave the cover on until the temperature rises above 50°F the next morning, then remove it so the plant does not overheat.

Plastic sheeting works in an emergency but has a drawback: it conducts cold and can damage leaves where it touches them. If you use plastic, place stakes or cages inside to hold it away from the foliage, or drape it over a frame so it does not rest on the plant itself.

Watering deeply the day before frost to warm the soil

Wet soil holds heat better than dry soil and releases that heat slowly overnight. Water your tomato plants deeply — until the water soaks 6 to 8 inches down — in the afternoon before frost is forecast. This does not prevent frost, but it raises the soil temperature slightly and can make the difference between a plant that survives and one that does not.

Do not water in the evening or at night. The goal is to give the soil time to absorb the water and warm up before temperatures drop. Morning watering is too late. Afternoon watering, 12 to 24 hours before the frost, gives the soil the best chance to hold and release heat.

Moving potted tomatoes indoors or to a sheltered space

If your tomatoes are in containers, move them into a garage, shed, basement, or indoors before the frost arrives. The space does not need to be heated — it only needs to stay above 32°F. A garage with the door closed, an unheated basement, or a covered porch will usually be warm enough. Check the temperature with a thermometer if you are unsure.

Move the pots in the late afternoon, before the temperature starts dropping. Leave them in the shelter until the frost has passed and daytime temperatures are back above 50°F. If the space is dark, the plants will not photosynthesize, but they can survive a few days without light. If you have a sunny window, place them there instead.

This method works best for small plants or a few pots. Moving a dozen large containers is labor-intensive and may not be worth the effort late in the season.

Using heat sources like lights or water jugs

A heat source underneath or near the plant can raise the temperature in the when ready area. String lights (incandescent, not LED) or a heat lamp placed under a row cover will generate warmth. Gallon jugs filled with water and placed around the base of the plant will absorb heat during the day and release it at night, similar to how watering works but more concentrated.

This method requires monitoring. Lights can overheat the plant if left on too long after sunrise, and water jugs are only effective if they have had a full day to warm up. It is most useful for a small number of high-value plants rather than a large garden.

Deciding whether to save plants late in the season

If frost arrives in late fall and your tomatoes are already producing fruit, protecting them may be worth the effort. If the plants are small, still flowering, or the season is nearly over anyway, it may make more sense to let them go and plan for next year.

Tomato plants that survive frost are often stressed and produce less fruit for the rest of the season. If you are protecting plants, focus on the healthiest ones with the most fruit already set. Weak plants or those with only flowers are less likely to repay the effort.

Recognizing frost damage and what to do after

Frost-damaged leaves turn black or dark brown and become mushy. Stems may also blacken. If you see this damage in the morning, the plant is dead — there is no recovery. Remove the dead plant from the garden so it does not attract pests or disease.

If your protection worked and the plant looks normal the next morning, remove the cover and resume normal care. Water the plant if the soil is dry, and monitor it for stress over the next few days. A plant that survived frost may drop some leaves or slow its growth, but it will usually bounce back if temperatures warm up.

Frequently Asked Questions

Can I save a tomato plant after it has been frosted?

No. Once frost damage occurs, the affected tissue is dead and cannot recover. The plant may survive if only some leaves are damaged, but blackened stems or widespread leaf damage means the plant will not produce more fruit. Remove it and start fresh next season.

What temperature should I start protecting tomatoes?

Begin protection when the forecast calls for temperatures at or below 40°F overnight. Tomatoes are damaged at 32°F, but they start to slow growth and weaken at temperatures below 50°F. Protecting them at 40°F gives you a safety margin.

How long can tomatoes survive under a cover?

A few days without issue. If the cover stays on longer than that, remove it during the day so the plant gets light and air circulation. Leaving a cover on continuously for more than three or four days can trap moisture and encourage mold or fungal disease.

Will frost cloth work if I leave it on all night?

Yes. Frost cloth is designed to stay on overnight and can be left in place until morning temperatures rise above 50°F. Remove it during the day so the plant does not overheat and so it gets full light.

Is it better to cover plants or move them indoors?

Moving potted plants indoors is more reliable because the temperature inside a building stays above freezing. Covers work well for garden plants but depend on how well you seal the edges and how cold the night gets. Use whichever method fits your setup — covers for in-ground plants, moving for containers.