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Clippings aren't to blame.
Thatch is a layer of dead and decomposing plant tissue that forms above the soil. A thin layer (½ to ¾ inch) is beneficial. It protects plant crowns and reduces compaction.
But if the layer gets too thick, water, air and fertilizer can't get through to the soil and grass roots. Runoff increases and dry spots appear. Or when it's wet, the thatch can remain saturated and suffocate roots.
Leaving grass clippings on the lawn when you mow does not cause thatch. Clippings break down quickly in most cases. Thatch is made up mostly of stems and roots that decompose more slowly.
Thatch usually occurs on turf that has been heavily fertilized, and is most common on poorly drained, compacted and acidic soils. Of the species of lawn grasses, fine fescues are most prone to thatch problems.
The best way to relieve thatch problems is by core aeration. Contract with a local landscape company for service or check with your local equipment rental center.
Core aerators punch small holes in the lawn, pull out the cores and leave them on the surface. Core aeration is most effective in late summer when temperatures are starting to cool and the soil is only slightly moist.
After aeration, air and moisture can penetrate the thatch through the holes. Leave the soil cores on the surface to dry. Then rake them to distribute the soil down through the grass to mix with and dilute the thatch. Don't allow the cores to wash away and pollute surface water.
The mixing action of core aeration is similar to that provided by earthworms. Core aeration can also help increase water infiltration on compacted soils.
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Website design: Craig Cramer cdc25@cornell.edu
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