By Tom Kalb, Horticulturist

NDSU Extension

Yikes! It is hot – dangerously hot. Our plants in the garden are wilting, and we are soaked in sweat trying to care for them.   

My cucumber and zucchini vines droop every afternoon. The initial harvest was great, but production is slowing down due to the extreme heat. The vines are producing fewer female (fruit-bearing) flowers. The pollen from the male flowers is less effective in this heat, too.

Bees don’t like this scorching heat. They are seeking shade and becoming less active pollinating our crops.

The combination of fewer female flowers, poor pollen and reduced bee activity will lead to a short-term reduction in production. I expect some of my next flush of cucumbers will be curled and misshapen because of insufficient pollination.  

Our tomatoes are suffering. When temperatures exceed 85 degrees Fahrenheit daily, tomato flowers may wither before setting fruits. Tomato fruits on the vine will be slower to redden and ripen.

We expect an uptick in more tomato fruits suffering from blossom end rot. This rot at the bottom of fruits is caused by a lack of calcium. Hot, dry conditions reduce soil moisture. When soil moisture is low, less calcium flows from the soil into the fruits, causing more blossom end rot.

Many peppers are getting sunburned. These scalded fruits are found on smaller plants that lack the foliage to shade the fruits.   

One way to combat excessive heat is to shade our plants. Shade cloth can be hung over them. Container plants can be moved to shady areas.

Adding mulch will conserve soil moisture. Be sure the mulch, whether it be straw or grass clippings, was not treated with herbicide.

Most of us respond to our wilting plants by irrigating them. Let’s discuss the proper way to irrigate your plants.

First, it is better to irrigate deeply and infrequently rather than giving your plants a sip of water every day. Roots grow where the water is. If you irrigate deeply, the roots of the plants will grow deeply. That’s what we want.

Next, irrigate in the morning after sunrise. Plants in the morning absorb the water they need, and their leaves will dry quickly. Avoid mid-day irrigation because you will lose much of the water from evaporation. Avoid watering at night because prolonged periods of wet leaves will lead to disease.

Do not use overhead irrigation. Why do we irrigate the leaves of a plant? A plant drinks primarily through its roots, not leaves. We should irrigate the roots. Wet leaves lead to disease.  

This reminds me of my first job: a sunflower killer at Northrup King Seed Company. The scientists at the company trained me to kill as many sunflower plants as possible with diseases. The goal was to discover a disease-resistant variety that I could not kill.

I grew diseases in the laboratory during the day and then sprinkled the disease spores on the plants at night. Then I turned on the overhead sprinklers. The presence of diseases along with wet leaves at night was a deadly combination.  

This deadly combination continues to work today. There is a huge outbreak of blight now on tomato and potato vines in my community garden. My fellow gardeners tell me this happens every year.

That’s because most of them wet the leaves of their plants when watering. Don’t do that! Instead, use a watering wand or soaker hose. Direct the water at the roots of the plants and keep the leaves dry.

Plants in our gardens are wilting today, but they can recover with your help. Irrigate early in the day, irrigate deeply and keep the leaves dry. Once this heat wave cools off, you may be rewarded with a bountiful harvest.

For more information about gardening, contact your local NDSU Extension agent.

NDSU Agriculture Communication – July 28, 2026

Source: Tom Kalb, 701-877-2585, tom.kalb@ndsu.edu

Editor: Dominic Erickson, 701-231-4435, dominic.erickson@ndsu.edu