Overwatering our lawns can promote diseases in turfgrass

Published on Wednesday, 14 June 2017 12:36 - Written by GREG GRANT, Texas A&M AgriLife Extension Service

Houston, we have a problem. Since starting to work in Smith County last fall, our office has been inundated with questions about lawn problems. One hundred percent of the cases have involved lawns that have been fertilized and were watered with automatic sprinkler systems.

Most of the problems have involved diseases of St. Augustine grass, including brown patch, gray leaf spot, and take-all root rot. The common denominator with all of these diseases is excess moisture. All are common problems in urban lawns with automatic sprinkler irrigation, and are rarely found in neglected lawns watered with hose-end sprinklers or not at all.

Water is the most cherished commodity in Texas these days, yet millions of gallons are wasted on home landscapes. While most are irrigating to improve their lawns, the reverse is often the result.

So how much and how often should one water a lawn in East Texas? It depends on how much it rains, your soil type and what grass you are growing, but basically, it amounts to an inch of water per week, minus rainfall. To be quite frank, if you are irrigating your lawn more than one time per week, you are probably wasting water and doing more harm to your grass than good.

I don’t even think about watering my lawn until July and August. In my professional horticultural opinion, other than severe droughts like 2011, properly planned landscapes in East Texas should rarely have to be irrigated during the fall, winter or spring. Those are the seasons when we generally receive adequate rainfall.

Grasses evolved on prairies, which receive moderate amounts of rainfall, in Texas generally 20 to 30 inches of rain per year. Most of East Texas receives 40 to 50 inches or rain per year. That’s why we grow forests here, not prairies. More irrigation than that is more suited for a rain forest, not a lawn.

In order for fungal spores to germinate on a grass plant, there has to be a film of water present. If a plant stays dry, there is no way for the spore to begin to grow. This goes for all plants.

A gentleman came into the office this past week with a sack of sick zoysia turf, the same kind of grass I have in my own lawn. He said he couldn’t stop the disease that was infecting his grass. My first question, “How often are you watering?” “Four times a week,” he said. Four times a week? I told him that was far beyond too much and that he was causing the disease. My same type of zoysia lawn gets watered about four times a year! My lawn is beautiful and disease-free.

I grew up mowing lawns and eventually worked at the turfgrass laboratories at both Texas A&M University and Louisiana State University. This wasteful and disease-stimulating overuse of water in the landscape has been a problem since the invention of sprinkler systems. The key to proper and helpful lawn sprinkling is to water deeply and infrequently. Deep watering promotes deep, drought-resistant roots, while infrequent watering reduces the incidence of diseases.

Water conservation in Texas will become more and more critical as the migration of new residents continues. When I was the county horticulturist in San Antonio years ago, I said that I thought there would come a day when we weren’t allowed to use water on our landscapes, and I still think that will eventually hold true. Smart gardeners are wise to learn to grow plants that survive on rainfall alone in each region of Texas. In the relatively moist environs of East Texas, it’s not that hard. By shutting off sprinklers during the fall, winter and spring we’d not only save millions of gallons of water but have healthier lawns and garden as well.

Greg Grant is the Smith County horticulturist for the Texas A&M AgriLife Extension Service. You can follow him on Facebook at “Greg Grant Gardens,” read his “Greg’s Ramblings” blog at arborgate.com or read his “In Greg’s Garden” in each issue of Texas Gardener magazine (texasgardener.com). For more information on local educational programming, go to smith.agrilife.org.