If your lawn has a bouncy feel to it when you walk on it, thatch
is probably building up. As a general rule, plan to dethatch your
lawn when the thickness of the thatch is more than 1/2 inch deep.
To determine the thickness, remove a small square of your lawn
to a depth of about 3 inches and measure the brown layer between
the grass blades and the soil surface.
For both cool and warm-season grasses, the best time to dethatch
is mid-to-late spring or early fall. During this time when the turf
is actively growing, the grass will quickly recover from injury.
The frequency of thatch removal depends upon how fast the thatch
layer builds. Lawns that are overwatered, overfertilized, or growing
on heavy clay soils may accumulate thatch quickly. Turfgrass species
is also a factor. Grasses such as bermudagrass, bentgrass, and Kentucky
bluegrass build a thick thatch layer over several months and may
need to be dethatched yearly. Grasses such as tall fescue and perennial
ryegrass do not produce much thatch and may not need to be dethatched
more than every few years.
to watch out for
Avoid dethatching when weeds are germinating to prevent them from
invading your turf. If you are planning to apply preemergence herbicides,
do so after dethatching. Otherwise, the herbicides may bind with
the thatch and decrease their effectiveness.