How to Care for Tomato Plants During Hot Weather
This July, much of Europe experienced an intense and prolonged heat wave, with temperatures reaching 104°F (40°C) in many regions. Although tomatoes are warm-season plants, prolonged extreme heat can still cause stress, leading to curled leaves, blossom drop, poor fruit set, and sunburn.
That is why we created this blog post covering everything you need to know about growing tomatoes in the high temperatures of summer to help your harvest.
What Temperature Is Best for Tomatoes
The ideal temperature for tomatoes during flowering and fruiting is 70°F to 85°F (21°C to 29°C) during the day and 60°F to 70°F (16°C to 21°C) at night. When daytime temperatures consistently exceed 90°F (32°C) and nighttime temperatures stay above 75°F (24°C), tomato plants experience heat stress.
Signs of Tomato Heat Stress
Wilting Leaves: High temperatures increase water loss, causing tomato leaves to droop or wilt. Plants may recover when temperatures cool in the evening, but persistent wilting may indicate severe heat stress.
Leaf Curling: Tomato leaves may curl upward in hot weather to reduce water loss and protect themselves from excessive sunlight.
Flower Dropping: Extreme heat can cause tomato flowers to dry out, become stressed, and fall from the plant.
Low Fruit Set: Extreme heat reduces pollen viability, leading to lower tomato yields. The plant may produce new flowers, but will not bear fruit under sustained high temperatures.
Sunburn: Strong sunlight and high temperatures can cause pale, yellow, or brown patches on exposed tomato fruit. Damaged areas will dry out, crack, and become sunken over time.
Slow Growth: Heat stress slows photosynthesis and nutrient absorption, resulting in slower growth.
Uneven Ripening: Prolonged high temperatures affect pigment formation, leading to uneven ripening of tomatoes, such as greening at the shoulders and lighter flesh color.
Heat-Tolerant Tomato Varieties
If you haven't bought your tomato seedlings yet, then choosing heat-tolerant varieties can help improve your chances of a successful harvest during hot summers. These varieties are bred to perform better in high temperatures:
- Ailsa Craig
- Big Beef
- Black Krim
- Costoluto Fiorentino
- Cuor di Bue
- Marmande
- Matina
- Roma
- San Marzano
- Tigerella
How to Protect Your Tomato Plants from Heat Stress
If your tomato plants have already taken root, then you'll need to take some external measures to prevent heat stress.
Provide Shade
During the sunniest parts of the day, especially during heat waves, providing shade can help lower leaf temperature, reduce water loss, and protect tomato plants from sunscald. For potted tomatoes, move the containers to a shaded area during intense afternoon sunlight. Once temperatures cool, move the pots back to ensure the plants receive at least 6 hours of direct sunlight daily.
For in-ground tomatoes, use a shade cloth to protect plants from strong afternoon sun. Choose a shade cloth with a 30% to 50% shading rate to reduce heat stress without blocking too much light. Use brackets to secure the shade cloth a few inches from the blades to improve airflow. Secure the bottom of the shade cloth with clips, stakes, or weights to prevent it from shifting in windy weather.
Water Frequent
During extreme heat, soil dries out faster, and tomato plants lose more water through transpiration. Increase watering frequency to help reduce heat stress. Don’t follow a fixed watering schedule. Instead, check soil moisture by inserting your finger 2–3 inches (5–7.5 cm) into the soil. If the soil feels dry, water deeply and thoroughly. On the hottest days, you may need to check twice a day.
If you have limited time for watering, consider installing a drip irrigation system. For in-ground tomatoes, drip irrigation can require more initial setup and investment, but it provides consistent moisture once installed. For potted tomatoes, small drip irrigation kits are affordable and easy to install; simply refill the water reservoir occasionally.
Mulching
Covering tomato plants with a 2-3 inch layer of organic mulch, such as straw, sawdust, leaf chips, compost, or grass clippings, helps lower soil temperature, reduce moisture evaporation, and alleviate heat stress. When laying the mulch, leave a 2-3 inch gap around the base of the stems to improve air circulation. Throughout the growing season, replenish the mulch as it decomposes or thins.
Improve Airflow
Increasing air circulation can help alleviate heat stress. When temperatures rise to 95°F (35°C) or higher, increase plant spacing to about 4 feet if conditions permit. For indoor potted tomatoes, place an oscillating clip fan nearby to blow air through the plant canopy gently.
Pruning can also improve airflow. Regularly trim dead branches and leaves from the lower parts of the plant, and trim excessive growth when needed. Avoid heavy pruning, as too much leaf removal can expose fruits to sunscald.
Early Picking
Harvest tomatoes early when the temperature is above 95°F (35°C) to protect them from heat damage. Tomatoes picked at the breaker stage can continue ripening indoors when placed in a well-ventilated area away from direct sunlight. Storing them with ethylene-producing fruits like apples can help speed up ripening. Harvesting in advance can not only prevent heat stress, but also prevent birds from stealing your harvest.
How to Recover Heat-Stressed Tomato Plants
If the damage is not too severe, heat-stressed tomato plants can often recover with proper care when the temperature cools down. Here are some practical measures:
Deep Watering
Heat-stressed tomato plants need immediate rehydration. Water slowly and deeply around the base of the plant to restore soil moisture. For potted tomatoes, water until excess moisture drains from the drainage holes.
Remove Damaged Leaves
Prune away dead, wilted, or severely damaged leaves to improve airflow and reduce the risk of disease. Avoid removing healthy leaves, as they are needed for photosynthesis, which provides the energy and resources the plant needs to recover.
Avoid Fertilizing
Do not apply fertilizer immediately after heat stress, as stressed roots may not absorb nutrients effectively. Wait until the plant shows signs of recovery, such as new leaf growth, before applying balanced nutrients if needed.
Be Patient
Heat-stressed tomatoes need time to recover. Continue regular care and avoid making sudden changes. Once the plant regains its health, it can resume normal growth and fruit production.
