During the summer, when people call or e-mail me, the subject turns to watering the lawn. Many tell me they water the three days they are allowed to each week. They are surprised when I tell them they can water seven days a week, but not from 10 a.m. to 4 p.m.
Things actually changed two years ago, when othe Georgia Environmental Protection Division started allowing daily watering, restricted by the times mentioned above. The restrictions are with a sprinkler system. You can hand water with a nozzle attached to a hose any time of the day.
How often should you water your lawn? My advice has always been to water it when it needs it and not on a regular schedule. Soil type, turfgrass variety, management level, frequency of rain, competition from tree roots, temperature, wind and humidity all affect the amount of water needed.
As many of you have discovered this year, there is a big difference between 92-degree and 106-degree days. When the temperature gets above 100, lawns may need watering twice or three times as often because they dry out so quickly.
Different soil types absorb and hold water at different rates. Clay soils absorb water slowly and stay moist longer than sandy soils that absorb water faster but dry out quickly.
Warm season grasses vary in drought tolerance. The order of drought tolerance (from best to worse) is Bermuda, St. Augustine, centipede and zoysia. Bermuda is far and away the most drought tolerant as it will grow a deep root system. Contrast that with zoysia, which has shallow roots and needs water more frequently.
The frequency of rain has a profound effect on watering. It’s amazing the difference in what rainwater does for the lawn compared to irrigation water. Rainwater probably lasts three to four times longer than irrigation water. You can get a 1-inch rainfall and, even with the extreme heat, you probably won’t need to water for at least a week, if not longer.
Put out 1 inch of irrigation water and it doesn’t seem to last more than two or three days. Get a rain gauge so you can keep up with how much it rains at your house.
On the management level, the more you fertilize, the more water is needed, because fertilizers have salts that raise water needs.
When it comes to watering the lawn, the starting point is 1 inch, once per week. We then make adjustments based on the previous factors.
The main mistake I see is light, frequent watering that produces shallow, weak root systems. A shallow root system prevents the efficient use of plant nutrients and soil moisture. Roots grow only where the soil is moist, they don’t seek out water. Watering for 15-20 minutes at a time with a rotary sprinkler wets only the upper inch or two of the soil. This in turn causes the grass to be much weaker and more susceptible to disease and insect damage. Most turf diseases are stress-related.
The key to success in watering your lawn is to condition the grass to get by on as little water as possible. The time to apply water is just before wilt occurs. Most grasses appear grayish and dull, the leaf blades fold or roll and footprints remain after walking over the area. If dry conditions continue, the grass will wilt. Water the lawn when the first symptoms of wilt begin to show.
Keep in mind that the length of time you run an irrigation zone is based on the type irrigation heads – gear- driven rotary heads and spray heads. Rotary heads put out a single stream or somewhat patterned spray as they rotate back and forth or 360 degrees, while spray heads put out a constant spray in one place. This means spray heads put out a lot more water in a shorter period of time. Most rotary heads put out 0.4 inches per hour, so even with good overlap it may take over an hour to put out 1 inch of water. Most spray heads will put out 1.5 inches per hour so you don’t have to run them nearly as long.
How do you know how much water to apply to your lawn each time? It should be enough to soak the soil to a depth of 6 to 8 inches. This is equivalent to an average of 1 inch of rainfall on an average soil. For sandier soils, a half inch of water may soak down that far, while it may take over an inch in clay soils.
Place some catch cans in various areas and see how long it takes to collect one inch of water. Then find out the depth of water penetration by using a soil probe or shovel. You can then adjust your system accordingly.