When you’re hot, you’re hot, especially if you are a tomato or a bell pepper and stuck in the ground.
There’s not a whole lot you can do to protect plants when the thermometer reads a scary 100°F or higher. Plants, like people, go into survival mode at this temperature. In order to stay alive, they shut down their productivity. The pollen in blossoms dries out and may become unviable. Flowers stop setting new buds. This is especially troublesome when evening temperatures stay above 75°F. Optimal growing conditions for tomatoes are daytime temperatures of 70°F to 85°F. Growth slows down at 86°F; it will stop at temperatures above 100°F. Cherry tomatoes and hot peppers are a little less susceptible to these conditions. Heirloom tomato varieties may suffer more. Beans, corn, cucumbers, eggplant, melons, peppers, and summer and winter squash are also susceptible to stress from high temperatures. Flowering perennials may slow down to a few blossoms.
While you cannot fix the weather, there are a couple of coping strategies you can employ. First, mulch the plants so the roots stay cool. Hot soil is just as bad as hot wind. Second, water all these plants deeply—generally once a week. This means the water should be soaking down to at least 6 inches in your soil. Take a trowel, shovel, or hori-hori knife and check that soil profile. A gardener’s mantra is to “water less often but deeper.” Fruit set should increase when temperatures moderate.
Flowering annuals seem to be the least affected by the heat. But they also benefit greatly from regular, deep watering. It’s good to deadhead spent blossoms so that when the heat wave passes, the plants will start setting flowers again. And they will look better for your efforts.
In the Mountain West, smoke from forest and range fires is another contributor to plant and gardener malaise. The smoke causes a significant increase in ozone, and there is nothing you can do about that. It’s best that you stay out of air like that. Get a glass of iced tea and wait it out. Autumn is just around the corner.
—Mary Ann Newcomer is the author of two books: Rocky Mountain Gardener’s Handbook and Vegetable Gardening in the Mountain States.