Michigan State University Extension
Ornamental Plants plus Version 3.0 - 00001565
11/12/99
Controlling Lawn Thatch
Thatch is a layer (Vis. 1) of undecomposed stems and roots
that accumulates near the soil surface. Grass clippings do
not contribute to thatch accumulation. The rate at which
thatch accumulates is determined by the type and vigor of
the grass in the lawn. A thatch-prone bluegrass sod, that
is given lots of water and fertilizer, forms thatch more
rapidly than other grasses given less care.
Thatch is a normal part of any lawn and only becomes
harmful when the thatch layer is thicker than 1/2 inch.
When thatch becomes excessive, the lawn may root into the
thatch rather than the soil. Thatch does not hold
moisture so lawns rooted into thatch will not tolerate dry
weather or cold temperatures. In fact, a very thatchy
lawn can be rolled up just like a rug when it dies out.
Thatch management can take several forms.
The easiest management technique is available to
homeowners with underground sprinklers. A 20 minute
watering at mid-day, every day, helps control thatch by
keeping it wet. Such a watering also is adequate for
watering the lawn.
Three other options are open to homeowners without
underground sprinklers. They are power rakes, coring and
topdressing.
Power rakes, or dethatchers, use power driven tines to
tear the thatch out of the lawn. Much of the lawn gets
torn out in the process. While this is the most common
way to dethatch, it is probably the least desirable.
Sections of very thatchy lawns may need to be reseeded due
dethatching injury. Early September is the best time to
use this type of thatch removal.
A more desirable alternative is coring. The limitation
here is the availability of the coring machines. Coring
machines remove cores of soil and sod. The hole allows
air and moisture to penetrate the thatch and help in its
decomposition.
A thin layer of soil can be applied over the lawn to
help decompose the thatch layer. This topdressing may
also be combined with coring. The soil introduces micro-
organisms that help decay the thatch.
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to commercial products or trade names does not imply
endorsement by MSU Extension or bias against those not
mentioned. This information becomes public property upon
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This file was generated from data base ZZ on 01/19/00.
Data base ZZ was last revised on 11/12/99.
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