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YARD AND GARDEN

September — an ideal time to remove thatch

Contrary to what you've been told most of your life, thatch isn't bad. However, too much thatch is bad, and that's what we need to look at.

First, the definition of thatch isn't black and white. There are as many definitions as there are types of lawns. Generally, thatch is the accumulation of dead roots and stems between the soil and turfgrass plants. It definitely is organic matter, and at times can contain some living plant material. Roots and stems contain a material called lignin that breaks down slowly.

Dave Robson

Notice that the definition does not include the word "leaves." Grass blades are composed mainly of water; during rapid growth, the leaf may contain 90-95 percent moisture. Place a leaf on the sidewalk during the summer and watch how fast it shrivels to nothing.

Thatch acts like the pad under your carpet. It cushions the turfgrass, preventing the grass crowns, where the growing point is located, from being compressed beneath your feet and the ground. Thatch acts as a thin layer of mulch, keeping the soil and moisture in. As thatch decomposes, it provides organic matter that earthworms and other beneficial soil organisms can feed on.

Problems start occurring when too much thatch is present.

When the thatch layer is greater than one inch, roots tend to migrate and stay in the loose thatch zone. It's an ideal environment for quick, easy growth. As long as the thatch stays moist, there's no problem. But when the thatch starts drying, and it dries first when the summer temperatures are hot, the grass starts wilting. Ultimately, the plants will die. Summer's temperatures, even with sufficient water in the thatch zone, can "bake" roots.

There's a greater chance of temperature extremes creating a problem, as thatch isn't the best insulator for plants growing in it. Winter injury is common.

Excess thatch can limit pesticide movement. Weed and insect control is limited. Diazinon, a common homeowner turfgrass insecticide, is an example.

Many diseases and insect problems are associated with excess thatch, including summer patch and leaf spot/melting out. Sod webworms prefer to live in the loose thatch zones; black cutworms also like a thatch layer, though they are seldom a serious problem. Grub damage, however, may be less, as female beetles prefer to lay their eggs in actual soil.

The only way to tell if too much thatch is present is to cut a core sample. Get down on your hands and knees and cut a sample roughly two inches in diameter and four to six inches deep. Measure the thatch layer.

There are many factors that can cause thatch accumulation, but the majority of the problems can be traced back to one factor — humans.

Most thatch develops because of poor cultural practices. Overfertilizing is key. So is excess irrigation. Both lead to heavy grass growth, and can result in heavy roots, rhizome, stolon and stem production. Since this material doesn't break down fast, thatch can build up.

Another key factor is poor mowing practices. Allowing the grass to get too tall and mowing more than one-third of the plant means cutting stems instead of just leaves. In the long run, the stems will collect and increase the thatch layer.

A compacted soil, the overuse of pesticides that could destroy soil organisms, and overwatering can also lead to thatch buildup. Some of the newer cultivars of bluegrass are more thatch producing than others. Tall fescues, zoysia grass and buffalograss can also produce excessive thatch.

Hand raking is one way to get rid of thatch. Dethatchers, usually called vertical mowers or power rakes, can also be used. The soil should be moist before using the machines.

Early September and early April are ideal times to remove thatch. Never remove more than one-half inch in the fall and spring or you may be destroying your entire lawn. Water and fertilize the grass after fall dethatching to stimulate recovery.

Remember, you can easily remove thatch, but you must remember to change your mowing, fertilizing, watering, or other cultural practices in order to avoid a perpetual problem.

David Robson is an Extension Educator, Horticulture, at the Springfield Extension Center, Cooperative Extension Service, University of Illinois. You can write to Robson in care of Illinois Country Living, P.O. Box 3787, Springfield, IL 62708. Telephone: (217) 782-6515. E-Mail: robsond@idea.ag.uiuc.edu

16 ILLINOIS COUNTRY LIVING SEPTEMBER 1998