Dethatching . . . Now, Later or Never?
Tim Seeber of Charlottetown, PEI, was just one of many people to ask lately about the process of dethatching — the act of removing dead grass and root tissue that builds up over the surface of the soil. Specifically, folks want to know if they should dethatch now, or wait until later in the season. And the answer isn’t “yes” or “no.” Careful consideration of several factors is important.
FIRST, THE DEFINITION OF THATCH — Here’s a passage from my book, The Organic Lawn Care Manual, that helps you understand what thatch is, or is not:
Thatch vs. Clippings: Remove One, Keep the Other
No matter what anyone else tells you, thatch and clippings are not the same things — and clippings do not cause thatch. Lawn thatch is the dead grass and root tissue between the green vegetation and the soil surface, which in layers of a half-inch thick or more will block water, air and nutrients from reaching the roots. Grass roots contain lignin, a substance that decomposes slowly and causes thatch. Grass clippings, the portion of the mown grass, are about 90 percent water, so they begin to decompose almost immediately after hitting the ground.
Many grass varieties in a traditional lawn care system can tend to build thatch layers quickly. Excess nitrogen pushes out excess top growth, but limits life in the soil and therefore slows decomposition of roots even more. The process of “dethatching,” either with a bamboo rake or power machine, removes this thatch that can then be gathered and composted.
Some thatch is common and acceptable in all lawns. Natural lawn systems that add life into the soil will rarely have issues with excess thatch. The beneficial microorganisms found in compost, compost teas and other forms of humus will feed on the thatch.
NOW, THE TIMING
If you have a thick layer of thatch, like the one in the photo above, you really have no choice other than to dethatch your lawn now. Heading into the heat of the season, water, fertilizer and air won’t be able to get to the roots and the lawn will certainly suffer the consequences. Renting a machine like the one shown above will be the least labor intensive way to complete the task. The mechanical tines break up and rake up the thatch layer so that the resulting material can be easily whisked up and gathered.
If you determine, however, that your thatch layer isn’t all that thick, it’s far better to dethatch in the fall when you won’t have so many weed seeds flying around.
The process of dethatching, whether done manually or with a machine, scratches the surface of the soil and will almost certainly wake up the weed seeds by exposing them to light. It’s essential, therefore, to overseed with grass seed right after dethatching. I then like to cover the grass seed with a thin layer of compost, which provides a mulch layer for the seed so it stays moist, and also blocks light from the crabgrass seeds that need light to germinate.
The only grass seed that needs direct sunlight to germinate is zoysia, so you’ll want to be sure to scatter that species of seed on top of the compost.
THE GOOD NEWS
As I stated in my passage in the book, organic lawns rarely if ever need dethatching after the first year of transition away from chemicals. The soil microbes will break down the thatch layer and keep it that way. In the place of thatch, you’ll have actively growing grass plants — which is the best defense against weeds.