Tomatoes Like It Hot, But Not Too Hot
Tomato plants are heat-loving plants that need 6 to 8 hours of sunlight a day but don't like scorching heat any more than the rest of us. When daytime temperatures soar into the 90s and hover in the 70s or warmer at night, tomato plants may keep blooming, but the flowers will fail to pollinate and then fall off. During extended periods of extreme heat, tomato plants can suffer severe stress and go into survival mode, putting all their energy into surviving rather than producing fruit. Even heat-tolerant varieties will slow down production in extreme heat.
Growing tomatoes in sweltering weather is relatively easy but does present a few challenges. Don't despair—there are several things gardeners can do to overcome the obstacles and help tomato plants remain productive throughout periods of steamy heat and humidity.
Heat Tolerant Tomatoes
Hundreds of tomatoes are suited to a wide range of growing zones from 3a to 11. As you would with all plants, select varieties well suited to your growing zone. In northern regions, tomato plants benefit from direct sunlight from morning to evening. But to survive and thrive during heat waves or in the South, where temperatures can get quite warm, tomato plants do best with morning sun and light shade in the afternoon. In warmer climates, tomatoes will not generally grow well in the sweltering heat of summer. Still, gardeners can grow them there during the mild winters. Some tomato varieties are more heat tolerant and better suited for warmer climates.
Some heat-tolerant tomatoes include:
- The 100-year-old heirloom Arkansas Traveler.
- Better Boy hybrid whose good foliage protection prevents sunscald.
- The cherry-sized Super Sweet 100 hybrid.
- Fourth of July hybrid.
- Quarter Century is heat tolerant and resists sunscald.
- Early Girl is heat-tolerant, prodigious producer of very early fruits.
Alternatively, gardeners can plant early-fruiting determinate varieties, such as the Early Girl hybrid, that ripen before the blistering summer heat sets in. As determinate tomatoes ripen at the same time, gardeners can harvest their entire tomato crop before the plants get stressed from the impending heat.
Mulch To Help Prevent Heat Stress
Mulch is the tomato's best friend during extreme heat. It insulates the soil, keeping it evenly cool and moist to protect plant roots from heat stress. To help conserve moisture and moderate soil temperature, apply a 2 to 3-inch layer of organic mulch such as compost, straw, chopped leaves or untreated dry grass clippings around the plant. Mulch also helps prevent moisture in the soil from evaporating quickly, inhibiting weed growth.
Provide Balanced Fertilization to Tomato Plants
Healthy soil is the foundation for a healthy garden. To take the guesswork out of it, test your soil every two or three years to get a complete picture of the nutrient presence and availability in the soil. Tomato plants need a steady balance of nitrogen, phosphorus and potassium to grow in addition to the trace elements zinc, copper, iron and sulfur. Rich compost can often supply a significant amount, and sometimes all, of a tomato plant's nutrient needs and will also improve soil structure.
Don't Fertilize During a Heat Wave
Don't feed tomato plants during a heat wave. When they are stressed and have gone into survival mode, they won't adequately absorb nutrients. Fertilizing, especially with nitrogen, during high heat encourages plants to grow; however, fertilization will produce more growth than the roots can support, giving way to leafy plants without much fruit. Excessive foliage growth also creates weak plants more vulnerable to insect and disease damage. Although tomatoes are relatively heavy feeders, excess fertilizer can burn the roots, establish a nutrient imbalance that causes problems such as blossom end rot, and ultimately diminish yield.
Maintain Proper Soil pH
Tomato plants do best in well-drained, slightly acidic soil with a pH of 6.2 to 6.8. If the pH is too high, amending the soil with lime can raise the pH level closer to the ideal balance. Test the soil's pH before adding lime. The proper pH balance will provide optimal nutrient uptake to prevent blossom end rot and premature tomato drop. Aim for balance. Just as over-watering plants can damage them, too much lime can raise the pH beyond 6.8 and block the plant's uptake of magnesium, a mineral that plays an essential role in photosynthesis.
Proper Watering Techniques in Hot Summer Weather
Tomato plants require 1 to 2 inches of water per week. Even with the most favorable conditions, tomato plants need regular watering to maintain adequate soil moisture. Water slowly, evenly and deeply at the base of the plant in the morning, and be careful not to get the foliage wet, which can invite disease. Soaking the plant deeply every few days is better than frequent shallow watering. Deep watering allows the water and the roots to sink deeper into the soil and helps the plants build robust and resilient root systems.
However, in extreme heat or drought or in areas with very light, fast-draining soil, gardeners may need to water tomato plants more often—daily and maybe even twice a day to keep the soil moist.
Water Consistently: Not Too Little And Not Too Much
Too little water can stress the plant, but so can too much water, and gardeners are at more risk of over-watering than under-watering. Over-watering causes the soil to become waterlogged, making it hard for air to reach roots, ultimately suffocating the plant. Too much water also leaches nutrients out of the root zone, damaging roots and encouraging disease.
Consistent moisture is vital. Inconsistent watering creates fluctuating moisture levels that can cause splitting, cracking and blossom end rot. Drip irrigation is an efficient and effective way to maintain a uniform soil moisture level. As tomato plants thrive in well-drained soil, allow the soil to dry out between waterings. To check if it's dry, stick your finger an inch or two into the soil. If it comes out clean, the soil is too dry and the plant needs water.
Plants will let you know when they're heat-stressed. Wilting and curling leaves resulting from heat and low moisture may indicate stress and signal that the plants need a drink."Physiological leaf roll" may result from disease; however, in hot weather, curling leaves likely represent the plant's efforts to conserve water. Watering wilting plants should revive them quickly.
The Importance of Weeding
Gardeners should weed before planting and then regularly to prevent weed growth. Weeds reduce fruit yield by competing for space, light, water, and nutrients, which can cause the plant to struggle and die. Some weeds may also serve as hosts for insects, diseases, or nematodes, subjecting the plant to damage. Properly preparing soil and mulching is the simplest way to suppress weed growth as it blocks the sunlight weed seeds need to germinate. To remove them without damaging the tomato plant and to avoid injuring the roots, remove weeds using a stainless steel weeder or Dutch hand hoe. These tools slice weeds off at the base and don't cause excessive root damage because, if used correctly, they only loosen the soil from about a quarter inch beneath the surface.
If weeding by hand, pull each weed individually from its base and slowly and steadily ease the roots from the soil. Be sure to remove the weeds entirely, including the long, sturdy tap roots. As many weeds can regenerate even from small pieces of root left behind, removing the whole undesirable plant is essential.
Picking and Pruning Tomatoes In Hot Weather
The Impact of High Temperatures on Tomato Ripening
Hot temperatures exceeding 85 to 90 degrees will significantly slow the ripening process or even stop the tomatoes from ripening. Excessive heat inhibits lycopene production, which gives fruit their typical ripe color. The tomato fruits will develop color on the outside but remain green on the inside and will not be as flavorful as when fully ripened. High temperatures during the ripening period and the resulting lack of lycopene may also cause"white core," a disorder in which the fruit develops a rigid, white tissue in its center.
Tomatoes Can Get Sunburned
Although tomatoes require a lot of heat and sunlight to ripen, light conditions have little to do with ripening. They do not need light to ripen, and fruit exposed to too much sun during prolonged periods of high heat may get"sunscald," the tomato version of sunburn. Effects of sunscald may include white or brown spots on the leaves and patches of blotchy white, yellow, or gray spots or cracks on the tomatoes.
The Problem With Over-Pruning Tomato Plants in Hot Weather
Don't over-prune tomato plants in sweltering weather. The plant foliage protects the fruit from the dangerous sun overexposure that causes sunscald and a condition known as"green shoulders." The upper parts of tomatoes, or the shoulders, generally receive the most sunlight exposure, offering some degree of sun protection to the lower part of the fruit. As a result, the more protected bottom part may ripen to red while the shoulders remain green. Removing more than a third of the leaves will eliminate the sun protection tomato plants need to avoid sun damage.
Consider Picking Tomatoes Before They Ripen to Red
In very hot weather, tomatoes will ripen more slowly or stop ripening. Be alert for the"breaker stage" or the"vine ripe" stage, when tomatoes begin turning their final color but are not completely ripe. Harvest tomatoes at this time before they are fully ripe and allow them to ripen indoors at room temperature, about 70 to 75 degrees. They will continue ripening off the vine indoors at a lower temperature and may even produce a better-tasting tomato.
When Temperatures Cool Down Again
All is not lost, as the negative effect on the plants is not permanent. When temperatures cool to the 80s, a healthy plant's vines will resume sending out more flowers and yielding late-season tomato fruits.
Employing a few previously mentioned strategies will assist in overcoming the challenges of growing tomatoes in high temperatures and allow them to remain productive throughout extended periods of extreme heat:
- Plant in locations that offer protection from too much sun exposure
- Avoid fertilizing during heat waves
- Add layers of organic mulch
- Water infrequently and deeply in the morning
- Weed regularly and carefully
- Don't over prune
- Watch for sun damage such as sunscald, white core, and green shoulders
- Pick the fruit early before it's fully ripe and allow it to ripen indoors
With proper care and attention to the weather, tomato plants will yield abundant bounties of luscious, flavorful tomatoes. Family-owned since 1876, Burpee has long been known for introducing innovative tomato varieties, including some of the most heat-tolerant tomatoes. Explore Burpee's wide collection of tomato seeds and plants, from the most miniature cherries to the grandest Big Boy Tomato.