Tomatoes are the divas of the vegetable patch — luscious, celebrated and notoriously hard to please. If it’s too chilly, they’ll sulk. If it’s too hot, they’ll throw a tantrum, scattering their blossoms and refusing to perform.
Gardeners everywhere know that planting tomatoes prematurely in spring is a mistake. They will just sit until the soil warms up. New transplants put in later will soon catch up and even overtake them.
The opposite problem — searing temperatures later on — is more complicated, and though hot, humid weather is weeks away, now is the time to prepare for the plants’ summer needs.
The tomato is a warm-weather creature. Although leaf crops such as lettuce, spinach and kale are most productive when it’s cool, tomatoes need plenty of warmth and sun to ripen those juicy red orbs.
But when temperatures rise into the 90s and above and stay there for a stretch of time, several bad things happen. The plants become stressed, desperately trying to pump water and nutrients through their systems as moisture evaporates from their leaves. Days of hot sun can cause sunscald, a disorder that produces whitish patches on the fruits and invites disease. The pollen in the plants’ small yellow flowers is ruined as well. Unable to make fruit, they fall to the ground.
For a home gardener, there are ways to cope with summer heat. Siting the garden in a spot that gets dappled afternoon shade from nearby trees will help a lot. Even a row of tall sunflowers might do the trick. Or you might erect a simple frame from wooden poles or metal pipe, to support sheets of black shade cloth with a 50 percent light transmission. The stakes, cages, fences or trellis you use to support the vines could have shade cloth draped over them until the heat wave passes. Just roll it up and keep it handy until needed.
Watering deeply and evenly will reduce heat stress. It will also help prevent cracking of the fruits and blossom end rot. Both can result from inconsistent irrigation.
A mulch will shade the soil, keep moisture in and keep pathogens in the soil from splashing onto the leaves. Drip irrigation is best, but if you use sprinklers, water at the beginning of the day so that moisture on the foliage evaporates promptly — another protection against disease.
How you prune tomatoes matters, too. Training them vertically, with a single stem, is often done to expose the fruits to sunlight for good ripening. With this method, any suckers that form in the forks where fruiting branches join the stem are pinched out. If you expect extra-hot weather, though, pinch higher up on the sucker to leave one pair of leaves to help shade the fruits.
Sometimes it gets so hot that the tomatoes never fully ripen. In that case, pick them when they’re not quite full colored and finish the ripening indoors.
There are heat-resistant varieties you can try. Grow a few and see whether you like them enough to replace your current favorites. But you can also grow determinates, a broad category that includes any variety that ripens a bountiful crop and then stops, unlike the indeterminate varieties that put out long, continuously producing vines. Determinates can be either supported or left to sprawl on the ground. In both cases, they’re easier to cover with shade cloth (or shade with sunflowers).
Simplest of all, there’s the two-crop solution: an early crop before it gets too hot and a later crop after the serious heat has passed.
Make the second crop a determinate variety, maybe one of the paste types that are so good for canning, freezing or drying. Plan for it to bear when the heat is scheduled to back off. Abundant fruits will appear just as it’s getting time to put them up for winter eating.
Barbara Damrosch is the author of “The Four Season Farm Gardener’s Cookbook.” Her website is fourseasonfarm.com.