Lawn thatch is a tight, spongy mass of non-decomposed organic matter, such as leaves, grass roots, stems, stolons and rhizomes between the soil surface and the grass blades. Thatch hinders grass growth, robbing it of nutrients and blocking water from reaching the roots. Thatch only becomes a problem when it gets too thick. There are measures to take to prevent thatch and methods to remove it.
To identify thatch, first look for dry and dead patches of lawn that have a sponginess to them. In several locations around the lawn, press your index finger into the grass to see if you can touch the soil. If you are unable to touch the soil, the lawn is affected by thatch. The next step is to measure the thickness of the thatch with a ruler by removing a plug of grass with a knife or trowel. If the thatch layer is thicker than 1/2 inch, you have a thatch problem.
While any lawn with any type of grass seed can be affected, thatch is especially fond of lawns that have been over-treated with chemical fertilizers and weed control products, according to Jerry Baker in "Jerry Baker's Green Grass Magic." Types of grass seed affected include cool-season bent grass; chewing, creeping red and hard fescues; Bermuda grass and warm-season Bermuda grass hybrid formulas; Kentucky bluegrass; zoysia grasses and St. Augustine grass.
To avoid thatch, there are a number of steps to take, including staying off the grass to avoid compacting the soil, mowing frequently, bagging all of the grass clippings, following recommended fertilizer rates, aerating the lawn every couple of years, watering deeply and letting the affected area dry out, and avoiding fast-growing grasses. Other measures to take include monitoring the pH level of the soil to ensure it does not fall below 6.0 and reseeding the lawn if the thatch problem is too severe.
Equipment to Remove Thatch
Thatch can be removed manually by using a cavex rake to cut through the organic matter. Power units such as a lawn mower with a de-thatching blade, a vertical mower or a power rake also work. A vertical mower's blades rotate vertically to cut into and remove the thatch, and there are power units that work as both vertical mowers and power rakes with interchangeable blades, according to "Lawns" by Nick Christians and Ashton Ritchie.
The best time to remove thatch in cool-season grasses is in the late summer, while the early spring is the best time for warm-season grasses. To remove thatch, first mow the lawn at the minimum recommended height for the type of grass and remove the clippings. Locate and mark all underground sprinkler systems and any utility lines buried near the surface. Over a period of several days to avoid damage to the lawn, remove thatch using the preferred equipment, making several passes perpendicular to each other to ensure the thatch is removed. After removing the thatch, fertilize and water the area to repair the grass.