Dry Weather Stress

By John Wilson

John Wilson

Our wet spring turned into a dry summer. At least we haven’t had extreme heat to make matters worse. Lawns, gardens and ornamentals are starting to show signs of our dry weather. Lawns starting to turn brown and wilting plants are the most visible signs. Low yields and poor quality vegetables are additional signs of heat stress.

Brown lawns are becoming a more common sight. Kentucky bluegrass has the ability to go dormant during summer to protect itself from heat and drought. This is what is happening when bluegrass lawns are turning brown… the grass is dormant, not dead.

To conserve water on turfgrass, it is fine to allow bluegrass lawns to go dormant. To keep them alive so they recover when cooler temperatures return, you should apply about a half inch of water every week or two, as needed, if you don’t get it from precipitation.

Fescue lawns are another story. You need to water them enough to keep them green… not golf course green… but at least a light green. Unlike bluegrass, fescue does not go dormant. If it turns brown, it enters a state which we call permanent dormancy… which is another way of saying it died and you will need to reseed the brown areas later this summer.

Ornamental plants and vegetables wilting during the heat of the day are also signs of plants protecting themselves from heat and drought. As long as the soil is moist and the plants only wilt during the day and then recover in the evenings, they are fine.

When plants wilt, you automatically assume they need water. In most cases they do, but check to see the soil is dry before watering. Larger leaved plants, like cucumbers, wilt during the heat of the day even when the soil is moist. This is the plant’s way of reducing the amount of water lost from leaves during the day. They do not need additional water… in fact too much water can injure them more than if you don’t water them at all.

Less obvious signs of heat and drought stress are bitter cucumbers, tomatoes with leathery brown bottoms, missing kernels in sweet corn ears, potato plants turning brown, poor fruit set, and the list could go on and on.

Most cucumber plants contain a bitter compound. When plants are stressed from heat, too little moisture, or poor fertility… bitterness in cucumbers is more prominent. Cucumber varieties listed as bitter-free or burpless are less likely to develop bitterness.

Bitterness is often limited to the stem end of the cucumber and the skin. Cutting off these portions will remove most of the bitterness. If the stress is severe, some cucumbers will be bitter all the way through and are best discarded. Even when pickled, they will remain bitter tasting.

When the bottom of a tomato fruit turns brown, this is blossom-end rot. It is caused by a lack of calcium in the fruit and peppers, squash and watermelon also can be affected. This deficiency is not due to a lack of calcium in the soil. It is result of factors that slow growth, such as heat or drought stress. To reduce blossom end rot, use mulch around plants, maintain uniform soil moisture and avoid overfertilizing with nitrogen.

If hot, dry conditions occur during pollination of sweet corn then pollination is often reduced. The results are sweet corn ears that do not develop kernels to the ear tip or have missing kernels throughout the ear. This sweet corn can still be eaten. Tomatoes with end rot can also be eaten if the brown portion is removed.

Some potatoes are turning brown due to hot air and soil temperatures. Once plants begin to die, harvest the potatoes. Even if there are not many potatoes or the tubers are small, once the plant dies tubers stop developing. If left in the ground, they are likely to rot.

For more information on watering your lawn or garden, contact your local UNL Extension office.