Tomatoes are one of the most popular plants to grow in home gardens. When cared for properly, tomato plants will reward you with an abundant harvest of delicious fruits all summer long. However, tomatoes do require certain growing conditions to thrive, including warm temperatures.
While tomatoes love heat, too much heat can negatively impact your plants. When temperatures soar above 85°F, tomato plants can become stressed, which leads to potentially disappointing results.
In this article, I’ll share how heat affects tomato plants, signs of heat stress, and most importantly – tips to beat the heat and keep your tomatoes happy even during hot weather.
How Does Heat Impact Tomato Plants?
Tomatoes are warm-season crops that prefer daytime temperatures between 70-85°F and nighttime temps above 55°F. However, just because tomatoes like warm conditions doesn’t mean extreme heat agrees with them. Here are the major ways heat affects tomato growth:
Impaired Photosynthesis
Like all plants, tomatoes rely on photosynthesis to convert sunlight into energy and fuel growth. However, the enzymes that drive photosynthesis are very temperature-sensitive.
When temps rise above 85°F, these important enzymes start to denature and lose function. With less active enzymes, photosynthesis grinds to a halt.
In turn, the plants have less energy available for essential growth processes. Development slows to a crawl.
Disrupted Reproduction
Tomatoes are classified as self-pollinating but still benefit greatly from bee activity. Pollen viability and transport dramatically decrease as temps reach 90°F and above.
Less viable pollen means many flowers fail to form fertile seeds. Blossoms end up aborting without setting any fruit. Photosynthesis may fuel growth, but pollination powers production.
Increased Transpiration
On hot days, tomato plants lose exponentially more water through leaf transpiration. They pump moisture out through pores in an attempt to cool down.
If this water loss isn’t adequately replenished via irrigation, the plants quickly become drought-stressed. This leads to wilting and potentially permanent damage.
Recognizing the Symptoms of Heat Stress
Signs of Heat Stress in Tomato Plants
It’s important to recognize the symptoms of heat stress in your tomato plants quickly so action can be taken before lasting damage occurs. Here are a few signs to look for:
- Wilting leaves – Tomato foliage will droop and appear limp if dealing with heat stress. The leaves may start to curl as well.
- Poor flowering and fruit set – Blossoms falling off and very few fruits developing on the vines indicate an issue with pollination related to the heat.
- Leaf scorch – Extreme heat literally burns the leaf edges, causing brown, crispy patches.
- Sunscald on fruits – Tomatoes exposed to full sun on very hot days can develop white or yellow patches on the skin.
- Slow growth – Both vegetative growth and fruit development will slow down significantly when temperatures rise above 90°F.
- Leaf yellowing – If heat is stressed for too long, tomato plant leaves will start to yellow from the bottom up.
Here are the stages of heat stress and what to look for at each level:
Mild to Moderate Stress
- Slight wilting or drooping of young leaves and shoots
- Blossoms slow to open, and remain closed during the day
- Blossom drop before fully opening without setting fruit
High Stress
- Severe wilting and curling of all leaves, even mature ones
- Leaves scorching around edges or tips
- Sunscald on green fruits before ripening (white patches)
Extreme, Prolonged Stress
- Wilted leaves failing to recover overnight; permanent limpness
- Leaves yellowing beginning with lower, older foliage
- Plant collapse as stem and branches go limp
- Browning leaves that turn crispy or drops off entirely.
Pay close attention during mid-summer heat waves and take action at the first signs of stress. Your tomato plants will thank you!
7 Tips to Help Tomato Plants Thrive in Hot Weather
No matter how high the mercury climbs, you can still grow amazing tomatoes by implementing a few simple techniques:
1. Provide Shade
One of the easiest ways to cool your tomato plants is by providing some shade, especially during the hottest part of the day. Options for shading include:
- Growing tomatoes on the east side of a structure that will shade them in the afternoon.
- Erecting temporary shade cloth structures over your tomato garden.
- Planting tomatoes near or under larger plants like corn and beans that offer dappled shade.
- Allowing leafy greens and herbs to grow around the base of your tomato plants.
A 40-50% shade cloth is ideal for tomatoes. Just a few hours of relief from the intense afternoon sun will help significantly.
2. Use Reflective Mulch
Applying mulch around your tomato plants serves multiple purposes, including cooling the soil and roots. A thick mulch layer insulates soil and roots from heating up excessively. It also retains moisture and suppresses weeds.
Opt for a reflective mulch like aluminum foil or white plastic sheeting rather than dark colors that absorb heat. The reflected sunlight bounces off the mulch instead of heating up the ground.
Mulching also conserves moisture and prevents weeds around your tomatoes.
I recommend 4-6 inches of straw or bark chips. Shredded leaves also work well. Grass clippings are okay, but decompose too rapidly.
3. Water Tomato Plants Deeply
Tomatoes need around 1-2″ of water per week from rain and/or irrigation. When it’s very hot, your plants will need more frequent watering to stay hydrated.
Focus on deep, infrequent soakings rather than frequent shallow sprinkles. Deep watering promotes stronger root growth, allowing your plants to better withstand heat and drought stress.
The best time to water is early morning, which allows the soil surface to dry out during the hottest part of the day. Use soaker hoses on a timer to target the soil. Avoid overhead watering that evaporates before penetrating deeply.
4. Avoid Excess Nitrogen
It’s easy to think that giving your tomato plants more fertilizer will help them grow better. However, over-fertilizing with nitrogen creates excessive, weak foliage growth that is more susceptible to heat issues.
Use a balanced fertilizer and stick to the recommended rates unless a soil test indicates otherwise. Too much nitrogen also leads to poor fruit quality and flavor.
5. Improve Air Circulation
Removing lower leaves and selective pruning opens up the tomato plant canopy, allowing for better air movement.
Good airflow keeps the humidity down and prevents foliar disease issues during hot, muggy weather. Set up large fans in your garden for extreme heat events to keep the air circulating.
6. Choose Heat-Tolerant Varieties
When selecting tomato varieties, look for heat-tolerant, drought-resistant cultivars that can better cope with high temperatures. Some great options include:
- Celebrity – One of the most popular hybrids that produces impressive yields even in hot conditions.
- Sun Leaper – A robust, large-fruited tomato bred to set fruit in temps up to 97°F.
- Solar Flare – This orange heirloom has fuzzy, heat-reflective leaves that help keep plants cool.
- Florida 91 – A heat-loving tomato that thrives in hot, humid climates.
7. Time Plantings for Cooler Weather
In areas with extremely hot summers, consider planting your tomatoes a few weeks later so they mature during cooler temperatures in fall. Or focus on growing tomatoes in spring and fall only.
You can also use season-extending techniques like shade structures, tunnel covers, and black plastic mulch to create a cooler microclimate around your tomatoes during summer.
Damage Control: Recovering Tomato Plants After Heat Stress Occurs
If you catch heat stress early, it’s often possible to nurse the plants back to health. Here are some tricks I’ve used successfully:
Emergency Shading
At first signs of wilting, shade plants heavily using whatever materials you have on hand – sheets, cardboard, tarps, etc. Continue for a few days after they perk back up as well.
Leaf Mist Cooling
Use an atomizer spray bottle to mist leaves frequently. As water evaporates off them, it has a cooling effect. Aim underneath leaves especially.
Solar Recovery Position
Gently bend wilted plants so affected leaves tilt away from direct sun. Stake stems loosely in this protected position until they recover.
Remove Damaged Growth
Prune off any totally shriveled, brown leaves or stems to reduce stress on the plant. New growth will replace them if recovery occurs.
Amend Surrounding Soil
Mix in extra compost around wilted plants to boost microbial activity and moisture retention. Side dress with worm castings too.
Frequently Asked Questions
At what temperature do tomato plants start to suffer from heat stress?
Tomatoes begin to experience impairment in growth and fruit production once temperatures exceed 85°F consistently. At 90-95°F, blossoms start to abort. Above 100°F, heat damage becomes severe.
Should I water tomato plants more frequently during hot weather?
Yes, tomatoes require more frequent irrigation during heat waves to replace the increased moisture lost through transpiration. Aim to deliver about 1-2 inches of water per week, and time watering for the early morning instead of the evening.
What type of mulch is best for insulating tomato plants from extreme heat?
Organic mulches like straw, bark chips, shredded leaves, or compost work best to maintain cool soil temperatures. Avoid black plastic mulch, which absorbs and transmits more heat. Reflective silver mulches can also help bounce heat away.
Conclusion
I hope this guide empowers you to grow tomatoes successfully in hot conditions. Understanding how heat impacts plants allows you to catch issues early based on subtle symptoms. Knowledge of preventative care and recovery tactics will serve you well when temperatures rise.
With adequate shade, mulch, and irrigation, your tomatoes can thrive despite summer scorchers. Be vigilant for any signs of heat stress, but don’t panic at the first hint of wilting. Just employ your arsenal of protective measures.
Here’s to a bountiful, climate-resilient tomato harvest this summer! Let me know if you have any other heat-beating tips to share.
