Stephen Henning wrote:
"J. M. Russo" wrote:

My lawn accumulates an excessive amount of thatch. Does
anyone know the cause of this, how to prevent it from happening
and how to get rid of the existing thatch as easily as possible.

These factors increase thatch development in grass by increasing
production of stems, leaf sheaths, and decay-resistant tissue:
1. choosing particularly vigorously growing grass varieties
2. applying excessive amounts of nitrogen, especially in spring
3. mowing infrequently or allowing grass to grow too tall
before mowing
4. growing varieties that are known to produce large amounts of
tough, fibrous tissue
5. compacted soil conditions leading to shallow root
development

Other contributing factors are factors that decrease the rate at
which thatch decomposes:
6. acidic soil conditions
7. pesticides that restrict micro-organism or earthworm
activity
8. allowing lawns to go dormant

Newer, improved varieties of Kentucky bluegrass that have been
developed for vigorous growth and better recovery on athletic
fields and high-quality home lawns develop thatch more quickly than
the less vigorously growing common types of Kentucky bluegrass.

Ways to prevent thatch include:

Fertilize only enough to maintain the lawn's desired color and
growth. Fall fertilization (mid to late October) is preferred to
spring fertilization because the resulting growth is not as rapid
and lush.

Compacted soils and soils with poor drainage tend to accumulate
thatch faster than well-drained soils. Aerification promotes better
moisture and air penetration into compacted soils. It helps
establish a deeper and healthier root system and also stimulates
the microbial activity involved in decomposing the thatch layer. To
be effective, the aerifier must have hollow tines or spoons that
bring the cores of soil to the surface.

Mowing frequency is determined by the growth rate of the grass. If
the desired height is two inches, grass should be cut when it is no
more than three inches tall - regardless of the mower used.

Avoid using pesticides as much as possible. Many pesticides affect
the microbial and earthworm populations that are involved in
decomposing the thatch layer.

Using a mulching mower will reduce the need for fertilizer.

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Travis in Shoreline (just North of Seattle) Washington
USDA Zone 8
Sunset Zone 5