You would think with all the rain and ground saturation that folks would know their lawns don’t need watering. But some people just don’t get it.
After last Saturday and Sunday’s 2 inches of rain, lo and behold, Monday morning there was a sprinkler running in a yard on my street. Several others were running early Tuesday morning in a nearby neighborhood I pass through coming back from the gym. I just can’t figure it out.
So having said that, let’s talk about how to water a lawn.
Let’s start with how often. My advice has always been to water a lawn when it needs it and not on a regular schedule. There are numerous factors that influence the amount and frequency of water needed for a lawn. Soil type, turfgrass variety, management level, frequency of rain, competition from tree roots, temperature, wind and humidity all affect the amount of water needed.
A huge factor is extreme heat. There is a big difference between 92 degrees and 106 (like we had for three days last year). When the temperature gets over 100, lawns may need watering twice or three times as often because they dry out quickly.
Another factor is the soil type. Different soils absorb and hold water at different rates. Clay soils absorb water slowly and stay moist longer than sandy soils, which absorb water faster but dry out quickly.
Our warm-season grasses vary in their drought tolerance. The order of drought tolerance (from best to worst) is Bermuda, St. Augustine, centipede and zoysia. Bermuda is far and away the most drought tolerant because it grows a really 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 when compared to irrigation water. Rainwater lasts longer than irrigation water. You can get a 1-inch rainfall and, even with extreme heat, you probably don’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, if you don’t have one, so you can keep up with how much it rains at your house. You can’t always go by what the meteorologists tell you has been recorded at Daniel Field or Bush Field.
On the management level, the more you fertilize the more water is needed, because fertilizers are salts and increase 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 only grow where the soil is moist, they don’t seek out water. Watering for 15-20 minutes at a time with a rotary sprinkler only wets the upper inch or two of the soil. This in turn causes the grass to be much weaker; therefore more susceptible to disease and insect damage. Most of our 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.
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 more than 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.
The best thing you can do to prevent your sprinkler from running when it is either raining or has rained a certain amount during the last few days is to install a rain sensor on your irrigation system. They make all types that you can buy at irrigation supply stores. The one used most often is the mini-click and cost in the $20-$25 range.
Sensors are particularly useful when you will be out of town for several days or for a week or two and want to leave the system on while you are gone.