Okay, I’m moving on up from underground rotted plant and animal remains that make up beneficial soil organic matter. There is often a layer of decomposing organics on top of the ground in lawns and other turf areas and it is not a good thing. It is thatch, a layer of dead turf grass “runners” that slowly builds up as time goes by. All of our major turf species are perennial plants. The same plant, root system and all, lives on year after year. But compared to such perennials as oak trees and azaleas, each individual grass plant has a relatively short lifespan. The good news is as grass plants die, sprouted replacements are already in place to take over. The bad news is the above ground “runners,” properly called “stolons,” are tough and very slow to decompose. It is these dead stolons that make up thatch.
Turf grass can tolerate some thatch without significant problems, up to about a half-inch layer. As thatch gets thicker, ill effects slowly set in. Think of thatch as pushing up living grass stolons, separating grass from ground. The grass lives on but its roots have to grow through the thatch instead of hugging Mother Earth. That means part of the roots are exposed to the extremes in temperatures. The plants become more vulnerable to the stresses of very cold, very hot and very dry. Usually grass doesn’t acutely croak from these maladies, but it is weakened for when the next bad thing happens. Often that next bad thing is disease. A thick layer of thatch makes for a happy home for several species of fungi that are problematic for grass.
A long term prevention plan for dealing with thatch is not difficult to write. When you plant or buy a lawn, plan to rent a dethatching machine every five years. Easy enough, but rare among us is the homeowner who will follow through. If the grass looks fine at age ten, most of us will leave it be. If it “ain’t” broke, don’t fix it. But for an existing bad layer of thatch that needs fixing, go with “better late than never.” Rent the dethatcher and give the lawn a good going over. Thatch cannot be conquered by fertilizer, irrigation or waiting until next year to see if it clears up.
Bagging lawn clippings at mowing time does nothing to prevent thatch. Mown grass leaves are mostly water and shrivel up to near nothing. They are not tough like stolons. But some folks prefer the fresh cut, bagged up look. So bag at mowing if you want, just know you are not preventing future thatch problems. Add clippings to the compost pile or use them as mulch. Or just pile them and they will shrink to near nothing. You could even drop bags of clippings over the front fence at my place. Just ensure there are no beer cans or jumbo styrofoam cups in the bag. I deal with enough of those from litterbugs.
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Terry Rector writes for the Warren County Soil and Water Conservation District, 601-636-7679 ext. 3.