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what causes thatch?

Discussion in 'Lawn Mowing' started by bobbygedd, Sep 20, 2001.

  1. bobbygedd

    bobbygedd LawnSite Fanatic
    from NJ
    Posts: 10,178

    i do alot of thatching in spring and fall, this year especially. i have a client who had us there to thatch and seed 3 yrs ago, lawn looked great. this spring he had us there to thatch, and hired us for fert program too. his lawn looked great all season, and still does, but there is considerable thatch build up again. we are gonna thatch again, y the heck does it keep coming back? what causes it?

    HOWARD JONES LawnSite Member
    Posts: 233

    Do a search "dethatch" - CMerLand post sounds like he knows the subject.
  3. guntruck

    guntruck LawnSite Senior Member
    Posts: 527

    I believe the thatch is a buildup of clippings. If it keeps building up than it is not breaking down fast enough and therefore you get the buildup. Try cutting the grass more often, remember, for best turf health you should cut no more than 1" of the blade of grass at any time. Although somewhat impractical if the clippings are too large that is slowing the decomposition process and causing the builup of thatch.
  4. Runner

    Runner LawnSite Fanatic
    Posts: 13,494

    While cutting no more than a third of the blade off is a rule of thumb, and help control the amount of clippings on the surface, this is mostly for the health of the plant, by reducing shock. Thatch, being the buildup of clippings faster than they can decompose, is actually fought by an enzyme that is naturally released by the rhyzomes of the grass. These enzymes help the clippings decompose faster. If the lawn is weak, the thinner it is, the less rhyzomes are in the subsoil. When there is high nitrogen content and lower rhizome count, (like with cheap fert. programs, i.e. nationals) this can certainly contribute to the problem. Infrequent cutting can certainly do it also, as if the clippings aren't chopped up enough, they take much longer to decompose. Hence, the buildup is faster than the decomposition rate. If you are having a consistant thatch problem, and your mowing practices are up to par, I would suggest increase your phos. and potassium, (at the right times) and build a thicker turf. Warning: You will have alot more grass per sq. ft. to cut this way. The results will be desirable, however. Also, there is a product out called Ringer Lawn Restore. This is basisically a granular that releases those enzymes that promote the decomposition of the thatch. Always remember, a little thatch is good. Another great way to control the buildup is regular aeration. This helps pull the thatch apart as the soil re expands and loosens up. When this happens, it thins it, and the thatch decomposes faster as well. I hope this helps.:)
  5. JimLewis

    JimLewis LawnSite Fanatic
    Posts: 6,841

    I will add that different varieties of grass develop thatch at different rates. Some varieties (like perennial ryegrass, which is the dominant type here in Oregon) break down thatch at about the same rate it accumulates. So there's little need for dethatching in perennial ryegrass lawns.

    There is great info about all of this as well as a chart that tells you which varieties develop thatch and how fast in the book called 'Turfgrass Management" by Turgeon. It's an excellent text on turf. In fact, it's the #1 text book on turf. It's spendy as heck ($90 or so) but you can find it on eBay once every week or so for about $5. That's where I got mine. Killer book for stuff like this.
  6. Got Vol. 5 here. Says that thatch occurs when plant biomass production exceeds decomposition...
    They just came out with the 6th volume this year. Also it talks about mat, which is thatch that has been decomposed more, and has been mixed in with the soil.
  7. kutnkru

    kutnkru LawnSite Silver Member
    Posts: 2,662

    There are many misconceptions about thatch, its causes, and problems.

    First, thatch is the dead and dying turfgrass plant parts, such as roots and stems. This layer develops above the soil surface and, in many cases, contains turfgrass shoots. Thatch is not the accumulation of clippings as some believe.

    A layer of thatch less than ½” does little, if any harm. However, when this layer is in excess of ¾” the turf is more susceptible to disease and insect problems and has less wear, drought, heat, and cold tolerance. Also, thatchy turf can be difficult to water as the layer can act as a water repellent when dry.

    Factors that lead to a thatch buildup are acid soils with a pH of less than 6.0, too little or excess fertilization, poor drainage, compacted soils, drought conditions, and overwatering.

    The only effective method of thatch removal is mechanical Dethatching. Biological and other chemical methods have proved to be ineffective and are not recommended.

    Topdressing is beneficial in reducing thatch. This will aid in the reduction of accumulation of the thatch layer. For larger areas where topdressing may not be feasible, you can core aerate and then either run a power rake over the cores to break them up, or work them back into the lawn with a metal drag mat or metal rake.

    Hope this helps.
  8. awm

    awm LawnSite Gold Member
    Posts: 3,354

    a lot of people dethatch when they really need light aeriation.
    ive checked all my accts ,and so far no real thatch to speak of.
    i consider dethatching necessary at over an eighth inch mat buildup. aeriation helps against compaction.
  9. kutnkru

    kutnkru LawnSite Silver Member
    Posts: 2,662

    AWM thats what alot of the fert companies in our area will tell clients. They will not even try to sell the power raking/dethatching that LCOs do.
  10. TGCummings

    TGCummings LawnSite Senior Member
    Posts: 773

    Thatch is not caused by a buildup of clippings!

    This is such an important point, and something I've been studying in my landscape class of late. Kris hit this point directly on the head with his post. It's an important distinction!

    When I first switched to mulching grass some years back, the first thing some of my customers asked me was "doesn't it produce more thatch?"

    Au contraire!

    Thatch is produced by growing grass! Organic material builds up between grass plants and soil surface all by itself.

    The only two things I would add to Kris' great post on this subject are:

    1) A layer of thatch 1/2" or less is actually beneficial to a lawn! It can insulate the grass against temperature changes, and

    2) Grasses that produce a lot of stem and crown tissue, such as Kentucky bluegrass and creeping red fescue, are the worst thatch producers. Rye and fescue grasses produce less because they grow in bunches with fewer stems.

    But, if you forget everything else, always remember the most salient point of this thread: Thatch is not caused by a buildup of clippings!


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