De-Mystifying Lawn Thatch

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Grass clippings decompose almost completely. That's the good news. What you should be concerned about is the partial decay of grass stems and roots that remain in the upper layers of your soil. These don't break down satisfactorily over time and contribute to a thatch layer that can affect the absorption of vital nutrients to support your lawn. When new grass cannot reach the soil, it sends its roots into the thatch, which has very little nutritive value.

When Thatch Becomes a Problem

Many homeowners like using vertical mowers to break up excessive thatch. But, according to lawn scientists with The University of Illinois Extension, if you habitually use too much nitrogen or over-water your lawn, the thatch will most likely return.

The extension suggests that core aerification is one of the best ways to treat excessive thatch when it accumulates in a layer of more than half an inch. Core aerators pull up deep plugs of lawn and soil--allowing nutrients to penetrate into the earth--and spread out the available access to soil across your lawn. The holes are typically spread out at a rate of 20 plugs per square foot of lawn. Since core aerators are often expensive to rent or in short supply, you may find it easier to contract with a lawn care service in your town to do the work.

The last step, the specialists say, is to apply a thin layer of soil top-dressing following the procedure to help in the breakdown of new grass clippings once you begin mowing again.