Drooping shrubs and brown lawns come with the territory during Georgia summers. While there’s not much that homeowners can do to perk up their plants in the short term, there are some ways to safeguard your landscape against long-term heat damage.
By the end of July, north Georgia has seen more than 30 days over 95 degrees Fahrenheit. South Georgia and middle Georgia haven’t fared much better, and there doesn’t seem to be much relief on the horizon.
That’s bad news for landscapes because plant cells start to suffer heat damage at 86 degrees. If the air temperature stays over 86 F for too long — especially if nighttime temperatures only dip into the upper 70s or low 80s — it can cause some lasting harm.
Plants vary in their ability to handle the heat, and if all of our landscapes were full of cacti, we would be in good shape. Unfortunately, three of the most popular plants in Georgia landscapes — hydrangeas, azaleas and dogwoods — are some of the first to show signs of drought and heat stress.
Signs of heat stress are fairly easy to identify.
Look around and you will see certain plants that have lost their green color and look yellowish, gray or just plain bleached out. Some leaves are showing scorched, brown areas, or they’re curling or wilting. Flowers are drying up or flowering may stop. It’s not just that these plants are dry; they’re too hot.
Wilt is the most obvious sign of extreme heat.
Plants transpire, just like we perspire, to help cool them off. Transpiration, or water evaporating from individual leaves, is the engine of the plant’s circulatory system. The vacuum created as water vapor escapes from a plant’s leaves pulls water up through the plant’s tissues, distributing nutrients. Water pressure keeps the green parts of plants firm and upright.
In the kind of heat we have been experiencing, the plants lose the water faster than they can take it up from the soil. This is especially true with herbaceous, or nonwoody, plants. Even irrigated plants will show signs of wilt.
Also, wilt isn’t always caused by a lack of water, as many people believe. In fact, too much water can show the same visual symptoms as too little water, so superirrigating to combat the stress of heat can also cause problems. Overwatering and under-watering both cause wilt.
Brother, can you spare some chlorophyll?
When it rises above 89 F, many plant functions, including photosynthesis, the process by which plants transform light energy from the sun into chemical energy, will start to shut down and plants will start lose their color. This is a sign that the plant is slowing down its production of chlorophyll, the molecule that makes plants green and enables photosynthesis. The problem will accelerate as temperature increases to 95 F.
There is no SPF for sunburned leaves.
Leaf scorch occurs when temperatures are too high and water is lost from leaves so fast that the internal plumbing can’t replace it. The edges and tips of leaves show scorch first, although whole leaves eventually can dry up.
Plant placement matters.
The location of your plants makes a difference. Plants next to a concrete driveways or patios that absorb and radiate heat will experience higher temperatures than what is indicated by a thermometer. I have already seen some damage to turfgrass growing not only next to driveways and curbs, but in other open, sunny areas as well. The grass has a tan or bleached look to it.
The same problem applies to your potted plants on a concrete patio. The only plants that are remotely happy are those in the shade.
So, what can you do when we are dealing with extreme heat?
Not a lot, but make sure you keep your plants watered. When you water individual trees and shrubs, don’t depend on a few minutes of sprinkler water. Watering lightly means the water won’t penetrate very far into the ground, and roots will grow only near the soil surface.
Give your plants a good soaking with a drip hose or hand water them. Water deeply to quench the thirst of the roots down within the subsoil and encourage deeper root growth. Deeper roots will help your plants better able to withstand drought conditions.
If your plants are not mulched, add some mulch to keep the plant roots cooler and to help conserve moisture. If they are already mulched, add more. Remember, gravel mulch actually increases the heat around plants, so this good time to invest in bark, leaf or pine straw mulch.
For more tips on preserving your landscape during droughts and heat waves, visit extension.uga.edu.