Lawn mowers perform a variety of valuable services in the landscape, but dethatching should not be one of them. While dethatching, or removing the spongy layer of dead, built up grass beneath the living grass blades, is a beneficial process for your lawn, using your mower to do it may cause harm to the machine.
Lawn mowers do not possess dethatcher blades equivalent to the functioning of a mechanical dethatcher, mainly because mowers work in a horizontal manner across the top of the lawn and vertical dethatchers, as the name suggests, punch down into the soil from above. You can attach spring tines to your mower, which will perform some of the same function, but according to the University of Kentucky Extension, they can cause severe mower damage. Purdue University Extension also advises you avoid any dethatching mechanism that attaches to your mower blade, rather sticking with specialized dethatching equipment.
Thatch isn’t all bad -- your lawn will actually benefit from a 1/2-inch layer of thatch to help reduce temperature fluctuations beneath the soil and provide a cushion for walking. More than that, however, can reduce water permeability and air movement and increase insect and disease problems. The best bet is to use a vertical dethatcher, which you may need to rent and that slices down through the top of the soil and brings up thatch with it. You can rent mechanical dethatchers from home and garden centers or specialists.
Dethatching the Lawn
Use the vertical dethatcher to reduce your thatch layer to about 1/2 inch. Make several passes back and forth across the lawn in both directions. Stop when either the thatch has reached the desired thickness, judging by eye, or when your lawn has holes larger than a few square inches. Any more and it might not recover, so even if thatch is still too thick, you should stop and plan another session after the lawn recovers. Be prepared for the lawn to look torn up for some time after dethatching. Depending on the degree of thatch removal necessary, the lawn may also require reseeding afterward.
If you have a serious thatch problem, it isn’t always possible to remove all the thatch at one time. Instead, focus on removing some of it without destroying the lawn, and then employ cultural measures. Provide regular lawn care such as watering and fertilization, and aerate your lawn using a mechanical aerator that removes core soil samples to allow penetration of air and water. Do not cut or slice the lawn, since this does not count as aeration and won’t help.
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