Thatch can be described as a tightly intermingled layer of partially decomposed stems, roots, and some leaves of grasses which develops beneath the actively growing green vegetation at the soil surface. Stems and roots of turfgrasses contribute primarily to thatch accumulations, while turfgrass leaves contribute little.
THATCH-INDUCED PROBLEMS
A thin layer of thatch, 1/2 inch, is desirable to add greater impact absorption on turfgrass areas, increase wear tolerance and insulate the soil from extreme temperatures. Excessive thatch accumulations (>3/4 inch) are undesirable because they decrease the vigor of turfgrasses by restricting the movement of air, water, plant nutrients, and other applied materials to the soil. During wet periods, thatch may act as a sponge and hold excessive amounts of water which can reduce the oxygen supply to the roots. During hot, dry weather, thatch may become dry and very resistant to wetting.
Turfgrass disease organisms and insects are harbored in thatch accumulations. Fungicide and insecticide effectiveness is reduced since the materials may not reach the pests.
Thatch may cause abnormal development of grass plants. Thatch accumulations are usually greater under high cutting management; hence, the grass stems may become elongated with the leaves forming at the top. Frequently, these leaves are mowed off and the lawn can appear brown, scalped, or off-color.
Mowing height is also affected by thatch accumulations. As undecomposed material builds up, the mower tends to ride on the thatch and does not cut at the desired height. If the cutting height is lowered in an attempt to overcome this problem, scalping and brown areas can develop.FACTORS CAUSING THATCH DEVELOPMENT
Thatch accumulation in lawns is influenced by the following factors:1. Mowing height. In general, the higher the
mowing height, the greater the tendency to
produce thatch. Mow grasses for the specific
height recommended for each variety and
geographic region.
2. Noncreeping, Colonial-type bentgrasses
develop more thatch than some bluegrasses,
perennial ryegrass, and fescues because of
their vigorous growth habits. A higher lignin
content in fescues, however, can lead to a
slower decomposition of vegetation matter
and increase in thatch accumulation.
3. Never use creeping bentgrass varieties for
home lawns because of the proliferation
of creeping stems (stolons). Creeping
bentgrasses are recommended only for
specialized areas, such as golf putting greens.
4. Crown tissues, stems, and roots are more
resistant to decay than leaves and contribute most
to thatch development in all grass varieties.
5. Nitrogen is required for growth and to
stimulate bacterial decomposition of thatch.
The other essential plant food elements, such
as phosphorus, calcium, magnesium, and
potassium, must also be present in the proper
balance as well.
6. Acid soil conditions (pH5) reduce bacterial
activity which may result in slow stem and root
decay, especially if calcium is deficient.
7. Overwatering causes a reduction in soil
oxygen and inhibits bacterial activity for
thatch decomposition. Saturated root zones
for extended periods will induce surface rooting
and enhance thatch accumulation.THATCH REMOVAL
Monitor the thatch depth. Practice thatch removal on an annual basis if necessary. If thatch becomes too deep in the lawn (>2 inches), renovation may be the only answer. Normal thatch removal will not injure the lawn severely enough to necessitate reseeding.
Timing. Early spring is the best period for thatch removal, particularly if large amounts need to be removed. At this time all dead surface debris which accumulate throughout the fall and winter can be removed. Turfgrasses are partially dormant at this time and the least amount of injury occurs. If properly thatched, lawn grasses will recover quickly and exhibit their normal beauty when conditions are suitable for growth. If light thatch removal is all that is required, thatching can be done any time of the year.
Power rakes, rotary mower attachments, or other mechanically driven thatch machines are superior to hand rakes. Considerable force is necessary to slice or scratch into the grass mat and remove all of the dead material. Less thorough jobs are done with hand rakes. Operate thatch machines across the turf in two opposite directions. Remove loosened material before changing directions.
Approximately 1/4 inch of thatch will be removed after going in both directions over the lawn. After thatch has been removed from the lawn, mow immediately at the recommended mowing height. Never increase the mowing height of lawn turf at any time during the season. There is no valid reason for changing the mowing height at any time during the year if the recommended height is practiced.
If thatch becomes unmanageable (over 2 inches in depth), it is best to remove all grass with a power sod cutter, cultivate the soil, and re-seed to desirable grasses.SUGGESTIONS FOR THATCH PREVENTION
1. Mow at proper height.
2. Maintain adequate fertilization programs for
normal growth. Nitrogen is important to stimu-
late heavy populations of bacterial organisms,
but do not overfertilize. A balanced program
is essential. (See EB0482, Home Lawns.)
3. Water thoroughly and infrequently, never light,
frequent irrigations. Do not overwater.
4. Check the depth of the soil and examine the
soil moisture content frequently during the
irrigation period.
5. Aerate the soil with hollow-tined aerifiers if
it becomes compacted or if water is not penetrating.
6. Maintain proper pH levels. If the soil becomes
too acid (5.5 or lower) light applications of lime
(calcium) may be beneficial to aid in thatch de-
composition. Use soil tests to determine this.
Good turfgrass management programs will help prevent thatch accumulations and maintain a healthy lawn. See EB0482, Home Lawns, for more details, or consult your local county extension agent.
