The Q&A Archives: Thatch Buildup in Zoysia

Question: I have a zoyia lawn, which is green until I mow, and then it turns brown. I have been told this is due to a build up of thatch. What can I do about it?

Answer: Have you determined that thatch is the problem? Zoysia has a moderately high tendency to form thatch, so it could well be the problem. Thatch is a layer of organic matter that forms between the grass plants and the soil surface, and consists of tightly woven living and dead grass stems, roots and crowns. These parts of the grass are very slow to break down, especially if the soil beneath is depleted of life (microorganisms, earthworms, etc.). Thatch blocks the movement of air, moisture, and nutrients, and can lead to shallow-rooted lawn grass, which is more likely to dry out during dry spells, and generally be less healthy, and more succeptible to disease and pests.

The best cure for thatch is proper soil/turf maintenance and good, healthy soil. Thatch can build up if you water shallowly or feed the lawn too much nitrogen (zoysia needs only 2-4lbs of nitrogen per year for good growth). Other contributing factors include infrequent, high mowing (zoysia should be mowed to 1-2" tall), excessive use of pesticides (kill off soil life that breaks down thatch materials), improper pH (target is 6.5-7.0), compacted soil or heavy clay (these two have less air in the soil, which slows organic matter decomposition).

So, first of all, you need to find out what may be leading to the thatch buildup in your yard. Test the soil pH, and also determine if aeration is necessary. If you regularly use pesticides on the lawn, try a different approach -- wait until symptoms appear so that you know pest are present. To build soil life, topdress with compost and spray the entire lawn with an "activating" product like seaweed/fish emulsion.

Here are some other steps useful for removing the thatch buildup:
1) scalp the lawn -- setting the mower as low as it will go and taking the grass to within 1/2 inch of the ground. 2) de-thatch -- using a rented machine the rakes the mat of runners right out (hand de-thatchers are available but they are not efficient and can wear out the best of us if the lawn is large). 3) aerate -- again, using a rented piece of equipment that removes small plugs of soil which you then fill in with composted soil.

Hope this helps!

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