Dethatching or 'Thatching'
Following season after
season of high
nitrogen lawn fertilization, most lawns develop a thatch layer. Up
to 1/2-inch thickness of thatch is considered OK, maybe even good. But
once thatch exceeds 1/2-inch in depth, problems begin with dead spots.
Some grass varieties, such as rhizome producing bluegrass, tend
to create thatch faster due to their growth habit. On the other hand,
lawns with red fescue are slow to build thatch, but that thatch is very
resistant to decay, creating a problem more slowly but one that is just
as severe.
You ask about mulching clippings? Mulching mowers rarely
contribute to thatch in normal situations,
at least ones where a heavy thatch layer doesn't already exist. However,
it would be a good idea to to bag clippings if you already have thick
thatch. Clippings breakdown best where they can make contact with the
soil.
Thatch prevention
beats 'The Cure'
There are several measures which can be practiced
annually, to prevent problems with thatch. These procedures are best
performed when turf is actively growing, preferably in the early fall -- September
in Pennsylvania --
- Aeration should be done
at least once annually (preferably twice -- spring and fall). Core
aerification involves "pulling plugs" from the lawn with a
hollow-spoon aerator and leaving them on the lawn surface to
breakdown.
- As thatch layers
get thicker than 1/2-inch, begin "thatching"
every year, with a mechanical dethatching machine, which removes dead
debris from the lawn surface. Some machines have spring tines or
flails, while others have vertical blades (known as vertical mowers or verticutters).
- Maintain proper soil pH
by testing your soil every 5 years. Follow soil test
recommendations. Attention to this detail will encourage
thatch to breakdown naturally.
This thatch layer made good cover
for destructive grubs
We've seen some real problem lawns
with thatch levels
exceeding 1-inch thick, and usually recommend stripping the lawn off
completely with a
sod-cutter, in order to start a brand new lawn from bare soil.
Reason: At this thickness, it would
take years to effectively reduce thatch thickness to a manageable level.
We
also recommend seeding your new lawn with improved varieties of turfgrass to
take full advantage of the advances in turf seed development. These will
be the more costly varieties that are "named" (read the seed label).
Aeration helps
control thatch
Liming helps break down thatch
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