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 there 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, as you’d expect from its tropical origin, 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.
Because I grow vegetables in a cool maritime climate, I’ve had this problem only once, when my tomatoes were in a greenhouse and someone unplugged the automatic venting system to plug in a radio. The temperature rose to 110, and as a result the plants struggled, even after they were able to grow new flowers.
Without such mishaps, tomato growers do use greenhouses successfully even in hot regions. Thanks to roof vents, shade cloth and evaporative cooling systems, a well-equipped greenhouse can offer shelter from the heat of high summer.
For a home gardener with no greenhouse, there are still 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. This would be true for any summer crop, but 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. (It also makes the vines more manageable.) 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, you’d want to 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 choose to 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, along with cabbage, collards and other delights of the cold season.
If your rosebushes were not pruned in late winter, you can tackle them now as a way of removing freeze-damaged growth. Remove congested canes to leave an open center and five or so main stems, pruned to just above burgeoning buds. New growth should soon hide the cold damage. An application of rose fertilizer or kelp feed will help them recover.
— Adrian Higgins