Tomato plants stop growing when nighttime temperatures drop below 55°F, and they die if frost reaches them

Tomato plants are warm-season crops. They need soil and air warmth to photosynthesize, move water and nutrients, and set fruit. Below 55°F at night, growth slows sharply. At 50°F, most varieties stop growing altogether. At 40°F or lower, the plant begins to suffer cellular damage. A hard frost — 28°F or colder — kills the entire plant, including the roots.

The exact threshold depends on the variety and how long the cold lasts. A cherry tomato might tolerate 45°F for a few hours. A beefsteak variety may be damaged at 48°F overnight. If the temperature hovers at 50°F for several nights in a row, the plant weakens even if it does not die outright. A single night at 32°F kills most tomato plants completely.

Key Takeaways

  • Tomato plants stop growing below 55°F at night and suffer damage below 50°F.
  • A frost event at 32°F or lower kills the entire plant, including roots that cannot regrow.
  • Covering plants with cloth, plastic, or row covers can protect them for a few hours during a cold snap.
  • Soil temperature matters as much as air temperature — cold soil slows root function even if the air warms during the day.
  • Hardening off seedlings by exposing them gradually to cooler outdoor air before planting reduces cold shock.

Why tomato plants cannot handle cold

Tomatoes evolved in warm climates and lack the biological machinery to survive freezing. Their cell membranes are fluid at warm temperatures but become rigid and rupture when ice forms inside the cells. Unlike cold-hardy plants such as kale or spinach, tomatoes have no antifreeze compounds in their sap.

Cold also shuts down the plant's ability to absorb water and nutrients from soil. Even if the air temperature rises the next day, a tomato plant that has been chilled overnight will not recover quickly. Repeated cold nights cause the plant to drop leaves, stop flowering, and eventually die from stress.

The difference between frost and a cold night

A cold night means the air temperature drops below 50°F but stays above 32°F. The plant slows or stops growing but survives. Leaves may curl or turn slightly purple (a sign of phosphorus stress from cold soil), but the plant will recover once warmth returns.

A frost event means the temperature reaches 32°F or below. Water in the plant's cells freezes, rupturing cell walls. Leaves blacken and wilt. Stems become mushy. The plant dies from the outside in, and even if the roots survive, the above-ground growth is lost. A hard frost below 28°F kills the roots as well, and the plant cannot regrow.

How to protect tomatoes from cold nights

If a cold night is forecast but temperatures will stay above 32°F, you can slow heat loss by covering the plant. Use cloth, burlap, old sheets, or commercial row covers — not plastic alone, which traps cold air directly against the leaves. Drape the cover loosely over the plant and anchor it to the ground with soil, rocks, or stakes so warm air trapped underneath does not escape.

Remove the cover the next morning once the sun warms the air, or the plant will overheat and weaken. This method works for a few hours of protection but is not reliable for a hard frost. If frost is forecast, the safest option is to harvest all mature and near-mature fruit before the cold arrives, then replant in spring.

Watering the soil deeply the afternoon before a cold night can also help. Wet soil holds heat better than dry soil and releases it slowly overnight, raising the air temperature around the plant by a few degrees. This small buffer sometimes makes the difference between survival and death.

Starting tomatoes early without cold damage

Many gardeners start tomato seeds indoors in late winter so plants are large enough to transplant outdoors as soon as the soil warms. The risk is planting too early. If you move seedlings from a warm indoor space directly into cold outdoor soil, the shock can stunt them permanently or kill them.

Hardening off — gradually exposing seedlings to outdoor conditions over 7 to 10 days — reduces this risk. Start by placing seedlings in a sheltered, shaded spot outdoors for an hour or two on a mild day. Each day, increase the time outside and move them into more direct sun. By the end of the period, they can tolerate a cool night without damage. Do not plant them in the garden until nighttime soil temperature is consistently above 55°F, which usually occurs 1 to 2 weeks after the last spring frost date in your area.

Soil temperature is as important as air temperature

Tomato roots absorb water and nutrients most efficiently when soil temperature is between 65°F and 75°F. Below 55°F, root function slows dramatically. Even if the daytime air temperature climbs to 70°F, cold soil prevents the plant from taking up water and nutrients fast enough to support growth.

You can warm the soil before planting by laying black plastic mulch over the bed for 1 to 2 weeks in spring. The plastic absorbs sunlight and raises soil temperature by 5 to 10 degrees. Remove the plastic once you plant, or the roots will overheat in summer. Alternatively, wait to plant until soil temperature reaches 60°F, measured with a soil thermometer pushed 4 inches into the ground in the morning.

Choosing cold-tolerant tomato varieties

Some tomato varieties tolerate cool nights better than others. Early-season varieties such as 'Siberia', 'Sub-Arctic Plenty', and 'Glacier' were bred to mature in short, cool growing seasons and can set fruit at lower temperatures than standard varieties. Cherry tomatoes such as 'Sungold' and 'Black Cherry' also tolerate cool nights better than large beefsteak types.

If you live in a region with cool springs or falls, choosing an early or cold-tolerant variety gives you a longer harvest window. These varieties typically produce smaller fruit or fewer total tomatoes than heat-loving types, but they will actually produce fruit in your climate rather than dropping flowers and refusing to set.

What to do if frost kills your tomato plants

If a hard frost kills your tomato plants in spring, the growing season is not necessarily over. Remove the dead plants and wait 1 to 2 weeks for the soil to warm again. Then replant with new seedlings or seeds. Many gardeners in cool climates plant tomatoes twice — once in late spring and again in midsummer — to avoid frost damage and still harvest before fall frost arrives.

If frost kills your plants in late summer or fall, the season is effectively over. Tomato plants cannot regrow from frozen roots, and new seedlings will not have time to mature before the next frost. At that point, harvest any green tomatoes and ripen them indoors on a windowsill or in a paper bag with a ripe banana or apple, which releases ethylene gas and speeds ripening.

Frequently Asked Questions

Can I plant tomatoes right after the last frost date?

Not safely. The last frost date is when frost stops occurring, but soil is often still cold. Wait 1 to 2 weeks after that date, or until soil temperature reaches 60°F. Planting too early into cold soil stunts growth and can kill seedlings.

Will tomato plants recover if they get cold but do not freeze?

Yes, if temperatures stay above 32°F. The plant will slow or stop growing for a few days, and leaves may curl or discolor. Once warmth returns, growth resumes. Repeated cold nights stress the plant and reduce total yield, but a single cold night usually causes no permanent damage.

Is it safe to cover tomatoes with plastic sheeting?

Plastic alone traps cold air directly against the leaves and can make frost damage worse. Use cloth, burlap, or row covers instead. If you use plastic, leave air gaps at the bottom so warm air can circulate, and remove it the next morning.

What temperature should soil be before I plant tomatoes?

Soil should be at least 60°F, measured 4 inches deep in the morning. Ideally, wait until it reaches 65°F or higher. You can check with a soil thermometer, or ask your local extension office for the typical soil warming date in your area.

Can I grow tomatoes in fall if I plant them in summer?

Yes, if you plant early enough that plants mature before fall frost arrives. Count backward from your first expected frost date — most varieties need 60 to 85 days from transplant to first ripe fruit. Plant in early to midsummer so harvest finishes before frost. Early and cold-tolerant varieties are your best bet for a fall crop.