How to Grow Tomatoes in Very Hot Weather

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Knowing how to grow tomatoes in very hot weather is mostly about keeping the flowers alive long enough to set fruit. Several extension pages agree that sustained heat, rather than one hot afternoon, is the trigger for lost blossoms, and their numbers differ a little. This guide uses those pages to explain what the heat does to the plant, which tomatoes cope best, and what you can change from the bed to the harvest basket.

Quick answer

Heat that lasts several days is the usual problem. The University of Delaware bulletin says hot days and nights “may cause blossom drop and fruit abortion in tomatoes.”
Choose heat-tolerant cultivars, since Penn State says heat tolerance “varies by cultivar, with some being more tolerant than others.”
Keep the water steady, water early in the day, and mulch the soil.
Shade cloth is one option that Penn State and Missouri mention, but the sources do not promise it will fix a severe heat spell.

Know the temperatures that stop fruit set

The sources do not agree on one number, so it helps to see them side by side. The Nevada fact sheet says that “Tomatoes grow best if temperatures range between 70- and 90-degrees Fahrenheit”. It treats daytime heat above 90 degrees as the main cause of blossom drop in its desert setting, and it notes that night heat can also abort flowers. The fact sheet is dated by its number, FS-88-60, so check current local guidance too.

The Delaware crop update describes a specific episode: “daytime highs 95°F and above and nighttime lows only getting down to 80°F” for several days in a row. Its figures show what a damaging stretch can look like rather than a fixed threshold. The Arkansas bulletin sets its own limit, saying that “During unfavorable weather (night temperatures lower than 55 degrees F or above 72 degrees F and day temperatures above 95 degrees F with dry, hot winds), tomatoes do not set fruit and the flowers drop.”

Penn State Extension says that fruit weight and the number of seeds per fruit are likely to be lower once temperatures go above 84 degrees F. The Missouri bulletin is broader. It says that “Warm season vegetables, such as cucumber, tomato, eggplant, pepper and green beans, grow best at temperatures of 68-86°F”, and that “Temperatures above 86°F will result in heat stress to warm season vegetables”.

The common thread is duration. Several days of high heat do the most damage, and a short spike is less likely to cause lasting harm. Tomatoes can tolerate short periods of extreme heat, but the Delaware page puts the risk plainly: several days or nights of high temperatures will cause the plant to abort flowers and fruit.

Why the flowers fall

A tomato flower needs to be pollinated quickly, and heat interferes with that step. The Delaware bulletin explains that “Normally in tomato fields pollination is achieved just by the action of the wind.” It adds that “Tomato flowers must be pollinated within 50 hours or they will abort and drop off.” When the pollen does not transfer in that window, the flower drops, and a hot spell can cause that loss across the whole plant.

Penn State describes a delay. It says that “When high temperatures occur 7–15 days before flowering, you’ll likely see aborted and dropped flowers”. It also says that “Flowers and fruit are more sensitive to high temperatures than leaves and stems.” That lag means the flowers you see may reflect heat from earlier in the month.

The Nevada fact sheet adds a nighttime cause. It says that “These sustained, hot temperatures at night burn up the food reserves the tomato produced during the day and the flowers abort.” Missouri describes the visible result on the plant. For a tomato plant with enough water in the soil, it says that heat stress shows up as “reduced plant size, low number of leaves, small and curling leaves, and dry flowers.”

Pick plants that handle heat

Cultivar choice is the first decision you can make before the heat arrives. Penn State says that “Heat tolerance in tomato plants varies by cultivar, with some being more tolerant than others.” Its advice is to look for heat-tolerant cultivars before the season starts.

The Arkansas bulletin points to a useful difference between plant types. It says that “cultivars, such as cherry tomatoes, set fruit during periods of high temperature that limit fruit production of the large-fruited types.” That statement suggests cherry types can keep setting fruit when the large-fruited types slow down.

Missouri is blunt about what growers can do in the field. It says that “There are no good ways to fight high temperatures in field.” That line is useful for setting expectations. Cultivar choice, water and shade help the plant cope, but none of the sources promises a full crop through a severe heat wave.

Keep the water steady and early

Steady moisture matters more in heat than most people expect. The Nevada fact sheet says that “Excessive irrigations and water stress also cause blossom drop.” That means both too much water and too little can cost you flowers. The same page says that “Tomatoes set best when humidity is between 40 and 70 percent.” Penn State adds that uneven soil moisture can also cause flowers to abort and drop.

The North Carolina Extension advice is simple: “Consistent watering is essential during the heat of summer.” It also says to “Water your plants in the morning when evaporation and temperatures are lower.” Morning water gives the plant time to take up moisture before the hottest part of the day, and it lowers the amount lost to evaporation.

The Arkansas bulletin gives a schedule for dry spells: “Water the plants thoroughly every two to four days during dry periods.” Its note for containers is that “Plants in containers need daily watering.” Use the schedule as a starting point, and check the soil before each watering. The Nevada fact sheet notes that “Tomato roots have a potential to grow to a depth of 3 to 5 feet”, which is one reason to water the root zone rather than only the surface.

The Nevada fact sheet also suggests a step for blossoms, saying that “Directing a strong jet of water at the blossoms twice during the heat of the day will improve blossom set” when day temperatures are in the 90s. The page does not explain its basis for that advice, so treat it as the source’s suggestion rather than a proven method. For hose attachments that help with watering plants, see hose attachments for watering plants.

Mulch and shade the bed

Mulch is the simplest change most beds can make. The North Carolina advice is that “Mulch retains moisture and keeps soil temperatures cooler.” A layer of mulch on the soil surface is one of the simplest changes a bed can make. For the bed plan itself, see vegetables to plant in raised beds.

Shade is the other common tool. Penn State says that “Installing shade cloth over the plants is another option.” The Missouri bulletin offers a similar idea for protected growing spaces, saying that “Shade cloth to cover high tunnels will ease the case.” That statement refers to high tunnels, so that advice does not transfer directly to a backyard bed.

Shade also helps with fruit quality. The Arkansas bulletin explains that “Poor color and sunscald occur when high temperatures retard the development of full color in tomatoes exposed directly to the sun.” Sunscald is the visible cost of that exposure. Penn State and Missouri both mention shade cloth as a heat measure, but the sources do not link shade cloth to sunscald directly.

Harvest often and expect a pause

When heat is strong, the crop may slow down, but you can keep the plant productive. The Arkansas bulletin advises that “During hot summer weather, pick tomatoes every day or every other day.” The sources do not say whether picking encourages more fruit, so treat frequent picking as a harvest habit rather than a fix.

The Nevada fact sheet says that “Tomatoes will produce again in the fall when temperatures cool.” It also notes that “Many gardeners give up on tomatoes when the plants stop setting.” A pause in fruit set during the hottest weeks is not necessarily the end of the season.

Mistakes to avoid

Letting the bed dry out. Nevada links water stress to blossom drop, and Arkansas recommends a thorough soaking every two to four days in dry weather.
Watering in the afternoon heat. North Carolina says to water in the morning, when evaporation and temperatures are lower.
Over- or under-feeding. The Nevada fact sheet says “High or low application rates of fertilizer will also cause blossom drop.”
Expecting a cultivar to solve everything. Penn State says uneven soil moisture and inadequate fertility can also cause aborted and dropped flowers.
Treating one hot day as the problem. Delaware says several days of heat, not a single hot afternoon, is the damaging pattern.

Frequently asked questions

How hot is too hot for tomatoes?

The sources give different numbers. Arkansas says unfavorable weather includes day temperatures above 95 degrees F with dry, hot winds, and night temperatures above 72 degrees F. Delaware describes daytime highs of 95°F and above with lows near 80°F for several days in a row. Penn State says fruit weight is likely to be lower above 84 degrees F. Treat these figures as warning levels rather than guarantees.

Why do tomato flowers fall off in the heat?

Delaware explains that tomato flowers must be pollinated within 50 hours, or they abort and drop. Penn State says high temperatures about 7–15 days before flowering can lead to aborted flowers, so the cause may be heat from earlier in the month. Nevada adds that hot nights can use up the food reserves the plant made during the day.

Is shade cloth worth using on tomatoes?

Penn State lists shade cloth as another option after cultivar choice. Missouri says shade cloth over high tunnels will ease the case. The sources do not give a shade percentage or a yield figure for a backyard bed, so treat shade cloth as one tool among several.

Will tomatoes set fruit again after a heat wave?

Nevada says tomatoes “will produce again in the fall when temperatures cool.” Penn State and Missouri do not give a fixed recovery time, so the cooling trend, rather than a date, is the best guide for when fruit set may return.

How much water do tomatoes need in extreme heat?

Arkansas gives a schedule of thorough watering every two to four days during dry periods. North Carolina says consistent watering is essential during summer heat and recommends morning watering. Nevada warns that both excessive water and water stress can cause blossom drop, so check the soil before you water.

How we chose

We chose the points that the sources state in plain words about tomato flowers, fruit set, heat and watering. The six pages are a Nevada fact sheet on tomato disorders in desert conditions, a University of Delaware weekly crop update, a Penn State Extension article on heat stress, a University of Missouri bulletin on heat-stressed tomatoes, an Arkansas tomato bulletin, and a North Carolina Extension article on high-temperature garden care. We read each page on 2026-10-22 and kept only the points that a page states, and we show the thresholds side by side because they differ.

What we could not verify

The pages give temperature thresholds in different units and with different conditions, so no single number fits every garden. The Nevada fact sheet and the Missouri bulletin describe conditions far from a typical backyard, and their advice on growers may not carry over. This article does not name a shade cloth, a sprayer, a fertilizer or any other product.

What the sources do not say

The sources do not give one daytime or nighttime figure that applies to every cultivar, and they do not say how many hours of shade a tomato needs. They do not give a shade cloth percentage for a home bed, and they do not give a yield loss figure for a given heat wave. Penn State’s advice to choose heat-tolerant cultivars does not name specific varieties. Check your local extension office for the heat patterns in your area.

Sources

https://naes.agnt.unr.edu/PMS/Pubs/1988-3266.pdf (opened 2026-10-22)
https://sites.udel.edu/weeklycropupdate/?p=6081 (opened 2026-10-22)
https://extension.psu.edu/heat-stress-and-tomatoes (opened 2026-10-22)
https://ipm.missouri.edu/mpg/2011/8/Heat-Stress-and-Heat-Stressed-Tomatoes/index.cfm (opened 2026-10-22)
https://www.uaex.uada.edu/publications/PDF/FSA-6017.pdf (opened 2026-10-22)
https://union.ces.ncsu.edu/news/how-to-care-for-your-garden-in-high-temperatures/ (opened 2026-10-22)