Sanjun Gu
Lincoln University
(573) 681-5313
Sanjun.Gu@luncolnu.edu
Published: August 1, 2011
Wrapping up July, 2011, I realized that I have never heard complaints about summer being not hot this year. Channel 17 claimed this summer one of the top ten hottest summers in record. So, "Is the excessive heat enough to 'cook' tomatoes"? The answer probably could be a "yes".
Warm season vegetables, such as cucumber, tomato, eggplant, pepper and green beans, grow best at temperatures of 68-86°F. Growth slows down significantly beyond 86°F and stops roughly above 104°F (Please note head index does not apply to plants). Temperatures above 86°F will result in heat stress to warm season vegetables (not for heat tolerant species such as Watermelon). The growth, development, biomass accumulation, and yield will all be adversely affected by heat stress although the damage depends on the crop's ability to withstand, acclimate, or recover from the stress. Heat stress is also closely associated with drought stress. The combination of heat/drought stresses kills or will kill a plant quickly.
For a tomato plant, when sufficient water is available in soil, visual symptoms of heat stress include reduced plant size, low number of leaves, small and curling leaves, and dry flowers. Fruit set is poor as pollen and stigma viability, anthesis, pollination, pollen tube growth, fertilization, and early embryo development are all highly susceptible to heat stress. Typically we would see a gap of fruit set along the plant (picture 1). Plants with some heat tolerance (picture 2) may set fruit, but fruit will be small and ripen early-cell expansion is inhibited but more plant hormone ethylene (responsible for fruit ripening) is released.
Picture 1: symptoms of heat stress. Note the fruit set change.
Picture 2: a heat tolerant cultivar with small fruit.
There are no good ways to fight high temperatures in field. Over head sprinkling would help to some extent to reduce air/leaf temperatures. This, however, has limited help under continuous and excessive heat condition, and may cause disease problems.
Shade cloth to cover high tunnels will ease the case. For plants to survive, water plants more frequently, about 2-3 times more. Growers can flood between rows in a raised bed system. Mowing weeds between rows instead of Rounding-up to keep moisture in soil. There are some tomato cultivars will survive better in high temperatures because of the built-in heat-tolerant genes, for example, some Florida and BHN series (Picture 2). Information on heat tolerant tomato varieties will be summarized later.
FAQs
When the cause of wilted tomatoes is dried out soil from heat, watering them will generally perk them up immediately. Apply water at the base of the plants avoiding the leaves or if using an overhead sprinkler, water in the morning to reduce the possibility of foliar diseases.
How do I protect my tomato plants from extreme heat? ›
Make some shade
To build one, create a simple frame around tomatoes using wood or row cover hoops, then drape shade cloth (found at garden centers or online) over it.
How often should I water tomatoes in extreme heat? ›
If there is a 100-degree forecast, check your plants at noon, he recommends. If they are wilted, that's a sign of stress. Give them a drink, even if that means watering twice a day. Plants naturally fold their foliage to reduce their surface area in high heat, so a little bit of wilt is of course going to happen.
Should you fertilize tomatoes when it's hot? ›
Don't fertilize during a heat wave. It just puts more stress on the plant. When you do feed them, stay away from high-nitrogen fertilizers; they'll produce luxurious vines but no tomatoes.
How long does it take a plant to recover from heat stress? ›
It can take anywhere from a couple of days to a couple of months for stressed plants to recover. Recovery time depends on the amount of damage that the heat caused to the plant. If a stressed plant is completely neglected during a heatwave, it can take several months or even be impossible to revive it.
Can tomato plants survive 100 degree weather? ›
Contrary to what many think, tomatoes are not heat lovers. They much prefer 75 to 95. When temperatures get too hot during the day (over 85 degrees) or are too hot overnight (over 70 degrees) many vegetables including tomatoes and peppers will drop their blossoms.
Do tomatoes need shade in extreme heat? ›
“The plant needs shade for developing fruit. Try to take the heat off from noon to 4 p.m. They need sun, they just don't need sun all day in 105 degrees.
Can tomatoes get too much sun or heat? ›
Yes, tomatoes can get too much sun. Too much bright direct sunlight on plants can raise temperatures too high for ripening and lead to cracking and sunscald. It can also create problems caused by high humidity or dry soil.
What temperature is too hot for growing tomatoes? ›
Actually, tomatoes like warm weather, between 65 and 85 degrees. When temperatures soar past 95, tomatoes stop growing. In that kind of heat, their flowers fail to pollinate and instead they dry up and drop off, putting a pause on the production of new fruit.
Is it better to water tomatoes day or night? ›
TOMATO WATERING TIPS
Water in the morning to the keep the soil moist through the heat of the day. Always water at the base of the plant — watering from above invites disease. Check tomatoes growing in pots often since they dry out quickly. Be consistent — fluctuations in water supply lead to cracking and blossom end ...
Water tomatoes in pots or raised beds frequently, as often as once or twice daily. Make sure the soil is healthy and well-draining, especially in pots and raised beds.
Do tomatoes like coffee grounds as fertilizer? ›
Coffee grounds contain around 2% nitrogen as well as varying amounts of phosphorus and potassium which are all very important for the growth of tomato plants. By mixing some coffee grounds into the soil below your tomato plants you're introducing these nutrients that the plants need to thrive.
What is the best fertilizer for tomatoes? ›
If your soil is well-balanced and composted, you can use fertilizers with NPK of 4-6-3. If your soil lacks nitrogen, use a more balanced fertilizer, such as a 10-10-10 NPK ratio, when plants are still developing. Opt for a fertilizer with lower nitrogen levels before the plants start fruiting.
Will damaged tomato plants recover? ›
Tomatoes are notorious for producing lots of “sucker” stems throughout the season, so you can count on something taking over for the lost main stem. You just need to be patient while the new stem develops. It will take a little time and there can be a bit of a growing setback — but it's usually not too bad.
Can plants recover from extreme heat? ›
Yes. Many plants can recover from extreme heat if they receive prompt care. The extent of recovery depends on the severity of the heat stress and the specific plant species. Some plants may suffer irreversible damage and may not fully recover.
How do you revive wilted tomato plants? ›
Plants may wilt badly when soils are dry, but will revive rapidly when they are watered. A thorough watering once a week during hot, dry weather should be sufficient. Apply water directly to the soil around the base of the plants with a garden or soaker hose.
