SerpApi.Org
Tomatoes are notoriously heat-loving vegetables, but even these hardy plants have their limits. While tomato plants are naturally adapted to warm, sunny conditions, long stretches of high temperatures can take a toll on them, leading to wilting, curled leaves, blossom drop and fewer tomatoes to harvest.
“You can tell by the layer of fuzzy hairs on their stems and leaves that tomato plants evolved in a dry climate,” says Frank Hyman, veteran horticulturist, expert tomato grower and author of Ripe Tomato Revolution. “They can tolerate some drought. But temperatures in the 90s and 100s? Not so much.”
Luckily, heat stress doesn’t always mean your tomato plants are doomed. In many cases, they simply need the right care to recover once temperatures stabilize. Here’s how to recognize the signs of heat stress, help your plants bounce back and know when it’s time to call it quits.
How to Tell if Your Tomato Plant is Heat-Stressed
Hyman explains that heat stress affects tomato plants in two main ways. First, extreme temperatures interfere with flowering and fruit production.
“Even when the plants are getting enough water, preferably from soaker hoses or drip lines running under the mulch, temperatures that high temporarily reduce fruit production,” he says.
Second, prolonged heat causes leaves to lose moisture faster than the roots can replace it, slowing growth and potentially damaging leaves and roots.
“Plants are somewhat like cold-blooded animals: a high temperature stimulates a thirsty, fast metabolism, while a low temperature slows down their metabolism,” he continues.
One of the easiest ways to determine whether your tomatoes are truly stressed is by checking them early in the morning. If the leaves are still wilted or curled after a cool night, the soil probably isn't providing enough moisture.
“Checking in the morning is important because wilting or curling leaves in the afternoon may just be caused by the momentarily high temperature, stimulating the leaves to transpire at a faster rate than the roots can gather water, even when there’s plenty of moisture in the soil,” Hyman says. “Wilting and curling leaves in the morning mean there isn’t enough moisture in the ground.”
Heat can also contribute to other common tomato problems.
“Blossom end rot and fruit cracking can also occur when watering is inconsistent during heat,” adds Jessica Mercer, horticulturist at Plant Addicts.
How to Revive Heat-Stressed Tomato Plants
Fortunately, there are several things you can do to bring your tomato plant back to life. Depending on how severe the problem is (and how long the heat lasts), you can try one, several or all of the following.
1. Water Deeply Instead of More Often
If your tomato plant looks heat-stressed, check the soil before watering. Stick your finger two to three inches into the soil near the roots. If it's dry, water slowly and deeply at the base of the plant.
“If the soil is wet and the plant is still wilting, don’t keep adding water, because waterlogged roots can also cause wilting,” Mercer says.
Continue watering deeply in the morning whenever the top few inches of soil dry out.
“Water long enough to moisten the root zone several inches down, encouraging the roots to grow deeper,” she says. “Keep in mind that containers, raised beds and grow bags dry out much faster than in-ground beds, so they may need daily water during a heat wave.”
2. Mulch the Soil to Keep Roots Cool
Adding two to three inches of mulch helps keep soil cooler and slows moisture loss during hot weather.
“The best mulch type for tomatoes includes straw, shredded leaves, compost and untreated grass clippings,” Mercer says. “Pull the mulch back a little from the stem. Mulch helps to stabilize soil temperatures and slow evaporation between waterings.”
3. Provide Afternoon Shade During Heat Waves
Temporary shade can help protect tomato plants during the hottest part of the afternoon. Use a shade cloth, patio umbrella or lightweight sheet, but avoid covering plants with heavy fabric that blocks airflow.
“You can also build an inexpensive frame,” Hyman says. “I recommend using rebar and tie wire to support a shade cloth that blocks 30% to 50% of the sunlight. If your schedule allows, only put the shade cloth up from mid-day to mid-afternoon when the sun is hottest. The rest of the day, the plants still need full sunlight to grow new leaves, flowers and fruit when conditions allow.”
4. Hold off Fertilizing
It may seem like fertilizer will give struggling tomato plants a boost, but feeding them during extreme heat can do more harm than good.
“Allow the plant to conserve energy and wait until temperatures cool,” Mercer says. “Once the plant starts growing normally again, you can resume feeding.”
5. Remove Only Severely Damaged Leaves
Skip heavy pruning during a heat wave since healthy leaves help shade fruit and prevent sunscald.
“Only remove yellow, diseased or badly damaged leaves, and leave the healthy foliage to shade the fruit,” Mercer says.
How to Tell If a Tomato Plant Can Recover
Many heat-stressed tomato plants recover if the stems remain flexible and some foliage stays green.
“The plant will likely perk up overnight or after a deep watering,” Mercer says. “Some yellowing and leaf loss is OK. Look for new growth after the weather improves.”
If the stems are brittle, the plant remains collapsed after watering or the base begins to rot, chances for recovery are slim. Mercer recommends scratching a lower stem to check for green tissue underneath.
“If the main stem and growing point at the top are still green, there’s still hope for good production as the season cools down,” Hyman says. “But if the top and main stem are brown, pull the plants and start over with something else.”
Sources:
- Frank Hyman, veteran horticulturist, expert tomato grower and author of Ripe Tomato Revolution
- Jessica Mercer, horticulturist at Plant Addicts
Related: Why Your tomato Plant Is Dropping Flowers—and What to Do About It
