A guide to helping vegetable plants survive July heat

The most noticeable effect of July’s high temperatures in our area is that plant growth slows or even stops as plants enter into a semi-dormant state in order to conserve moisture and energy. Plants have other normal reactions to heat stress, but often these normal reactions worry home gardeners who think they’re doing something wrong.

▪ Some vegetables including eggplants and peppers can tolerate high heat and will continue to flower and remain productive in the garden during the summer months.

Tomatoes and beans are more heat-sensitive; they drop their flowers when temperatures are regularly above 95 degrees.

▪ Pole beans (Kentucky Wonder, Romano) have a longer productive season than bush beans (Blue Lake) and pole bean plants often recover from heat stress later in the summer to set a new crop. Bush beans finish their productive season when the first really hot spell hits. Pull exhausted bush beans now and replant seeds in late August for a cooler-season fall crop.

Heat-stressed beans, both bush and pole types, are especially susceptible to pest insect problems including whiteflies, aphids and mites. Insecticidal soaps generally provide good control for many pest insects but read labels to verify that the soaps can be applied when temperatures are high. Save up your water allotment to blast pest insects off plants when temperatures are too high to spray insecticides.

▪ Tomatoes will begin to flower and set fruit again in late August. In the meantime, keep your tomatoes well watered. Tomato plants require approximately 5 gallons of water each week. Tomato plants often wilt during the heat of the day-it’s a normal reaction. However, if daytime wilting continues into the cooler night, supplement irrigation with a bucket of shower water.

▪ Members of the cucurbit plant family include squash, melons and cucumbers. Cucurbits produce both male and female flowers on the same plant.

Bees, not the wind, are the primary pollinators of cucurbits. They carry pollen from the male to the female flowers. Bees slow down their foraging for pollen when temperatures are high. When the tiny immature fruit at the base of the female flower is not pollinated, it withers and dies. Incomplete pollination, when there are few bees, causes deformed fruit and low yields. Pollination on squashes can be done by hand using a clean artist’s brush to move the pollen from inside the male flowers (longer straight stems) which appear first on the plant to inside the female flower (stem looks like a tiny fruit). However, high temps also cause cucurbit flowers to wilt quickly, making even hand pollination difficult. (Note: seeds for hybridized parthenocarpic or self-pollinating cucumbers and zucchini that don’t need bees or male flowers for pollination are available; these new hybrids are also seedless).

During the worst of the summer heat, plant leaves curl up in an attempt to slow moisture loss.

▪ Citrus trees are the first to curl their leaves during hot spells. Deep irrigate citrus trees whenever their leaves are curling and check inside the curled leaves (on any plant) for aphid infestations which also can cause leaf curling.

This story was originally published July 8, 2015 at 9:10 AM with the headline "A guide to helping vegetable plants survive July heat."