Selecting Varieties for Heat Tolerance
Getting crops through summer heat takes several tactics at once. Cultural practices like shade, irrigation, mulch and good post-harvest handling are essential, and they're covered in detail in our summer heat series. Alongside those practices, choosing the right varieties matters just as much. Trials in hot locations around the country help reveal which varieties cope best with heat stress.
Definition of “Heat Tolerant”
A heat-tolerant designation means a variety holds up comparatively well in hot weather compared with others of the same crop. It's most meaningful for crops that usually struggle in heat, as opposed to warm-season crops that thrive in it, and it's meant to steer growers toward better choices.
Search or filter for "heat tolerant" to find these varieties.
When browsing, look for "heat tolerant" in the variety description.
What Makes a Variety Heat Tolerant?
Trials of both cool-season and warm-season varieties compare how they perform, yield and taste under high heat.
Cool-Loving Crops
What counts as heat tolerance depends on the crop and type. For cool-season crops, it means varieties that handle more heat than standard ones. Even the most heat-tolerant cool-season varieties may not survive truly extreme heat, such as summers in the Southeast, Southwest, Deep South and Florida.
'Fujiyama' was bred to make good-quality heads in warm weather.
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Broccoli:
Varieties without heat tolerance bolt, sending up flower stalks before the heads fully mature. Heat-tolerant broccoli forms heads with deep green color and even beads that stay marketable for a few days, and even when heads get oversized they still look good enough to sell. -
Cauliflower:
Heat-tolerant cauliflower forms attractive, firm heads with good color rather than turning yellow or purple. Its curds also stay smooth, fine and firm instead of quickly loosening and getting fuzzy. -
Greens:
In greens, heat tolerance means better-than-average resistance to bolting under stress. For red varieties especially, it can also mean holding good color in heat, since rapid growth and strong light can wash out some varieties. As with other cool-season crops, even the most heat-tolerant types may not handle extreme heat, so good cultural practices are still needed. -
Lettuce:
In lettuce, heat tolerance means better resistance to tipburn and bolting under day and night heat while keeping the expected head shape. Many heat-tolerant lettuces also grow faster. Still, no lettuce can handle extreme heat on its own; cultural practices are needed for a healthy crop. Note too that a heat-tolerant rating refers to summer conditions (hot days and nights), and for some varieties, particularly heading types, it may not carry over to spring or fall, when temperatures swing from cool to hot or hot to cool. -
Radishes:
Radishes that lack heat tolerance turn oval and get pithy fast in warm weather. Heat-tolerant radishes stay round, firm and crisp in warm weather, even when a bit oversized. All radishes get hotter and harsher-tasting in heat. Specialty and Asian/Daikon/Korean radishes usually handle heat very well, since they were developed in hot, humid regions, and they make great hot-weather alternatives to small round radishes.
'Sora' is an organic, heat-tolerant variety with high-quality roots.
Warm-Loving Crops
Tomatoes and cucumbers generally love warmth, but extreme heat stresses them too. Heat stress can make flowers drop, cutting yields, and sunscald can ruin fruit for market.
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Cucumbers:
Heat-stressed cucumbers may drop many flowers and set less fruit. Heat-tolerant varieties tend to hold onto their flowers better at high temperatures than other cucumbers. -
Tomatoes:
Heat-stressed tomatoes may drop many flowers and set less fruit. Heat-tolerant varieties tend to hold onto their flowers better at high temperatures than other tomatoes.
'Jolene' is a smooth, deep red beefsteak that keeps setting fruit in heat that stops other tomatoes, and it carries TYLCV resistance, useful for growers in the Deep South.
