Thirsty Plants, Hot Days - Why Are These Numbers Important? 89-95-86
THIRSTY PLANTS, HOT DAYS - WHY ARE THESE NUMBERS IMPORTANT?
89 - 95 - 86
People who regularly irrigate their lawn and garden have asked me what is wrong with their plants. They assume that by keeping them watered, plants should be fine, but in the kind of heat we have been experiencing, plants lose water faster than they can take it up from the soil. This is especially true with herbaceous (nonwoody) plants.
Look around and you will see plants that have lost their green color and look yellowish or gray or just plain bleached out with leaves showing scorched brown areas, curling, wilting, and flowers drying up or no flowering at all.
Plants transpire, just like we perspire, to cool off. Not only does water help plants transpire, it runs the whole system. The vacuum created as vapor escapes pulls water up through the plant tissues, distributing nutrients. Water pressure keeps the green parts of plants firm and upright.
Water is also necessary for photosynthesis. Photosynthesis is the process by which plants transform light energy from the sun into chemical energy that drives a plant's growth processes. Chlorophyll is the molecule that converts sunlight, water and carbon dioxide into a usable form of energy or glucose. So the less water, the less photosynthesis occurs.
When the temperature rises above 89 degrees, most plants burn chlorophyll quickly; the green can disappear and plant functions will start to shut down. The problem will accelerate as the temperature increases to 95 degrees.
Another crucial number is 86 degrees. That's the temperature at which plant cells start to suffer damage. If the air temperature stays above that point for a long period of time, especially if it doesn't fall much at night to give plants relief, it can cause lasting harm.
We all know that plants vary in their ability to take the heat. Three of the most popular plants in the landscape are among the first to show signs of heat stress: Hydrangeas, azaleas and dogwoods. Other plants, including pine trees, yaupon hollies and dwarf nandinas, are more heat tolerant. If our landscapes were full of cacti, I guess we would be in good shape.
Leaf scorch occurs when temperatures are too high and water is lost from leaves so fast the internal plumbing can't replace it. Edges and tips of leaves show scorch first, although whole leaves eventually can dry up.
Wilt is the most obvious sign of extreme heat, but wilt isn't always caused by a lack of water, as many people believe. In fact, too much water can cause the same visual symptoms as too little.
The location of your plants also makes a difference. Plants next to a concrete driveway that absorbs and radiates heat will have temperatures much higher than what is on the thermometer. Same thing applies to your potted plants on a patio. The only plants that are remotely happy are those in the shade.
In periods of extreme heat, keep your plants properly watered. When you water trees and shrubs, give them a good soaking with a drip hose or hand water them. Water deeply to get the moisture to quench the thirst of those roots down within the subsoil. This encourages deeper root growth and makes your plants better able to withstand drought.
To avoid fungus problems that come with heat and humidity, it’s best to avoid putting your plants to bed wet. Try to water early enough that plants can dry before it gets dark.
You may want to add some mulch to keep the plant roots cooler and to help conserve moisture. If they are already mulched, add more if needed. Use organic mulch. Gravel actually increases the heat around plants.
