Home & Garden

Protect flowering plants from withering heat

The oppressive summer heat and humidity are upon us! The extended forecast predicts temperatures in the mid- to upper-90s for the foreseeable future.

Not only is this uncomfortable for us, it can be devastating to our plants — particularly when the heat is accompanied by a lack of rain. Many of our colorful spring flowers are showing signs of intense stress.

When daytime temperatures reach about 95 degrees, the ability of plants to make carbohydrates for growth begins to decrease. High nighttime temperatures compound the problem because plants don’t have time to rest, much like the effect that long periods of sleeplessness would have on our productivity. They increase the rate of breaking down these carbohydrates, and the plant has to use its energy reserves to just to keep itself alive.

Plants have the ability to cool themselves through a natural process called transpiration, in which water is “pumped” out through its leaves, similar to our bodies producing sweat. However, if the root system is inadequate or not enough water is available, this process stops. Plants wilt and possible leaf scorching results.

University of Georgia horticulturists recommend doing everything possible to conserve soil moisture and prevent root injury.

Whenever you water, do it deeply and infrequently. This encourages roots to move deeper into the soil and helps plants survive times of drought stress. As a general rule, 6 gallons of water per 10 square feet of bed area will wet the soil to a 12-inch depth. Frequent, small amounts of water will lead to shallow root systems more likely to suffer in the heat.

The best way to deliver water to your garden is with a drip hose that applies water to the ground near the plants without wetting the foliage. If an overhead sprinkler is used, water early in the morning to minimize evaporation and discourage disease problems. Use fine-textured mulches — such as pine straw, pine-bark mini nuggets or shredded wood mulch — to hold moisture in the soil.

Avoid fertilizing drought-stressed plants with fast-acting fertilizers. Chemically, they are salts that can pull water from the roots, further dehydrating them. Don’t disturb the roots by digging, or cause soil compaction near the roots by walking in the area when the soil is damp.

Keep annuals and herbaceous perennials from setting seeds, which competes for the plant’s food supplies. Remove spent blossoms from the plants before seeds mature. If they are showing significant environmental stress, cut them back to within 6 inches of the ground. Most will return with vigor, assuming they get some moisture to sustain what growth is left.

Make a note of flowering plants in your garden that are performing well in the heat, so you can include them in next year’s garden. Some heat-tolerant color suggestions include lantana, zinnia, portulaca and vinca.

For now, take a break in the shade with a cold lemonade and know that cooler temperatures are coming — just not soon enough!

Contact county Extension agent Karol Kelly at karolk@uga.edu.