Thatch is a layer of under-composed stems, roots, leaves, and debris that accumulates between the above-ground stems (stolons) and the soil.  This layer can compress, and is called a mat; as this layer thickens, the grass roots may root into the mat, rather than in the ground.  Lawns rooted in this manner may have dead spots during extremely dry or cold periods.

There are two ways to get rid of thatch.  The first method is to not allow it to develop in the first place, while the second is to remove it.  Following proper mowing procedures will help keep thatch from occurring.  These procedures are discussed further in the mowing section. 

We recommend that you attempt to remove thatch only when the lawn is brown in the winter.  First, lower the mower one notch lower and bag clippings.  This step will remove brown leaf blades and under-composed plant debris.  If you don’t bag the clippings, they will just go right back to form more thatch and mat.  Second, rake hard with a regular leaf rake and remove litter.  Some mowers have “tine rake” attachments, which flick out thatch, which is then bagged by the mower.  Third, core aerate the lawn.  This process removes cores of soil and deposits them on top of the ground.  By allowing more air movement, remaining thatch is decomposed aerobically.  Core aeration also improves drainage, increases root depth, and relieves soil compaction.  Core aeration helps to modify thatch by adding soil to the thatch layer.  This step allows soil bacteria to aid in the breakdown of the thatch layer.  We offer this service in the late fall.

Never power de-thatch your lawn with hook blade attachments or power de-thatchers, such as vertical mowers.  These machines can only be used on rhizome-forming turf grasses, such as Bermuda grass and Zoysia grass.  They can also be used on clump-type seeded grasses like Kentucky 31 fescue.  Centipede grass and St. Augustine grass do not form rhizomes (below-ground stems), and form only stolons (above-ground stems).  Using power de-thatchers set too low can remove not only the thatch, but also the lawn itself.