Edible Gardening

Growing Veggies in Summer Heat


There are several vegetables in the garden that thrive during the long days of summer—tomatoes, peppers, eggplant, squash, cucumbers, beans, field peas and corn to name a few. However, when the days become so hot you feel as if you are walking on the surface of the sun and the nights are not much different, those poor vegetable plants have no relief.

The only way plants can deal with summer’s heat is through transpiration.  Transpiration is the process of water evaporating inside the leaf and moving out of the stomata (small holes in the leaf surface). This cooling effect of the water evaporating inside the plant is like sweat evaporating from your skin. Unlike you and I, plants can’t walk into an air-conditioned room to escape the heat.

When temperatures are over 90 degrees many plants will wilt. This is because the plant can’t take water up fast enough through their roots to keep up with the transpiration in the leaves. This type of wilting will usually go away as the temperatures drop in the evening.

A more permanent effect occurs in the flowers when daytime temperatures exceed 90 – 95 degrees F and nighttime temperatures don’t drop below 70 – 75 degrees F. This effect is a disruption in the cell division process that makes the pollen. The disruption results in sterile pollen that cannot fertilize the flowers. Ultimately, the result is that fruit set declines or stops in some vegetable crops. The effect is worst when temperatures stay in this range for more than seven days. Research has indicated it is the high nighttime temperatures that have the most effect.

As an extension agent, I often receive calls during these hot summer months from gardeners wanting to know why their tomato or pepper plants look green and healthy, are flowering really well, but they are not producing any fruit. The short answer to this question is, “It’s just too hot!” If the plants appear healthy, but just aren’t producing fruit a break in the heat will often bring an abundance of fruit.

The online publication “Tomatoes in the Florida Garden” has a list of tomatoes that will produce well in the Triangle heat, including Better Boy, Duke, Solar Set, Celebrity, Suncoast, Homestead, Beefmaster, Beefstake, Sweet 100, and Sweet Million.

Shawn Banks is the Consumer Horticulture Agent with the NC Cooperative Extension Service in Johnston County.  You may reach him at shawn_banks@ncsu.edu.

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