"Thatch removal efforts should be undertaken only when conditions favor rapid recovery of turfgrass. Spring and late-summer/early fall are the best times to remove thatch. While several machines will remove thatch, a vertical mower (also referred to as a power rake) is the preferred device. Unlike rotary lawn mowers which drive a blade that is on a horizontal plane to the surface, vertical mowers propel a series of
knife-like tines on a plane that is perpendicular to the surface. The tines should be adjusted so that a bit of soil is brought to the surface together with the thatch.
"De-thatching using a properly adjusted vertical mower will produce an astounding quantity of stems and other plant parts which must be removed from the lawn. Before running the vertical mower over a lawn, consideration must be given to disposition of the debris."
Above excerpt from <a href="http://www.cas.psu.edu/docs/coext/regions/southeast/berks/mg/hgargd/turf_thatch.htm">PA Coop Extension document<a>
See also
http://www.agry.purdue.edu/turf/pubs/ay8.htm
>There are dethatching machines to remove thatch. The Purdue site recommends a sod cutter

for 1" or more of thatch. Both the PA and Purdue sites state that a vertical mower, with
fixed blades or tines, is the preferred machine to use for lesser amounts. If you have ever used a
vertical mower with fixed blades, cutting through the thatch to the soil, you know what lawn destruction is! Most dethatching, or powerraking, we see done in the springtime is done with vertical flail type machines. The flail type "dethatchers" do not do anything to remove thatch, you need a fixed blade machine to honestly sell a thatch removal job, and it's gonna be a mess when you are done. Aeration is a much more preferable remedy.
----------
Jim
North central Indiana
[Edited by GroundKprs on 09-08-2000 at 03:29 AM]