What Temperatures Can a Tomato Plant Tolerate?

Extreme Temperatures

• Tomato plants begin to lose their blossoms if exposed to daytime temperatures above 85 degrees Fahrenheit. Tomato plants can stop producing flowers if exposed to temperatures above 104 degrees for four or more hours. If the daytime temperature reaches 85 degrees and the nighttime temperature drops to 55 degrees or rises to 75 degrees, the tomato plant's pollen becomes tacky and pollination stops.

Optimal Temperatures

• Tomato plants grow best when daytime temperatures average between 70 and 85 degrees. Tomatoes ripen best when temperatures are between 68 and 77 degrees. Temperature plays an important role in the ripening of tomatoes. When temperatures move beyond the optimal zone, the ripening process ceases because the tomatoes can no longer produce the enzymes lycopene and carotene, which give the fruit its color.

Subarctic Tomatoes

• Some varieties of tomatoes have been altered to grow in temperatures lower than the optimal zones. Subarctic tomato plants are usually not available from nurseries. Home gardeners who want to grow subarctic tomatoes will need to plant seeds instead of seedlings.

Protection

• Several precautions can be taken to help tomato plants survive and bear fruit during extreme temperatures. Covering tomato plants with plastic, sheets or row covers during frost or excessively cold weather can prevent them from dying. Row covers also protect tomatoes against heat caused by direct sunlight. Do not let the covers rest directly on the plants or completely cover them because this will have a greenhouse effect and generate more heat. Some airflow helps cool the plants.