Thatch grass when the thatch layer, consisting of undecomposed stems and roots, becomes thicker than a half-inch, recommends the Michigan State University Extension. While you can use a power rake in early September, a coring machine causes less damage to the lawn.
About this Author
Rogue Parrish has written two travel books and edited at the "The Baltimore Sun," "The Washington Post" and the Alaska Newspapers company. She began writing professionally in 1975. Parrish holds a summa cum laude Bachelor of Science degree in journalism from the University of Maryland.