Note: About Thatch

"Thatch is light brown, fibrous organic matter that looks like peat moss. It is located between the soil and grass blades and is made up of compressed surface roots, stems, and runners. Thatch is hidden, so most people do not realize it is there. Excessive thatch feels soft and springy underfoot. " -Matthew J. Fagerness [13]

Checking for thatch
Checking for thatch is easy. All you need is a study jackknife. Start by cutting a pie-shaped wedge out of the lawn, making sure to get down into the soil.

Pull the wedge out, and examine the brown mat of thatch just above the soil surface.

Replace the wedge and examine other places in your lawn. Just because thatch is present or absent in one place doesn't mean the same will be true in another. Thatch thickness typically varies throughout the lawn. Places where thatch has gotten thick feel soft and spongy when you walk across them.

From info source Division of Cooperative Extension of the University of Wisconsin-Extension, Item # 535 Thatch (Viewed 6 Apr. 2004)

Photographs illustrating thatch