A: Dethatching is done in the early spring to early summer; the second choice would be to do it in early fall. Because dethatching stresses grass, do it when the grass is growing best, not in the heat of summer or during a drought. Everyone’s got some thatch. It depends on how finely the grass is cut all year, how long it is allowed to grow before cutting, the regularity of raking, and the weight of snow cover on the lawn during winter.
Usually it is not necessary to dethatch every year. Check first — dethatching is hard work. You can check to see whether your lawn needs it by cutting into the sod and seeing how deep a thatch layer exists. Anything more than about a half-inch, and you could use a dethatching.
Dethatching can be done by machine. You can rent a power machine or do it by hand, using a firm rake. Both methods accomplish the same end — they remove the layer of dry, dead vegetation, which, if left to accumulate, will hinder the absorption of water, fertilizer and weed-control chemicals. Without dethatching, weed killers and fertilizers will just run off and never reach the soil and roots. When left in place, thatch also provides a cozy breeding place for bugs and grubs.
To prevent thatch from reoccurring, use a thatching mower, which cuts the grass blades into fine pieces. You can also accomplish this with an ordinary mower by repeated mowing over the cutting area, to chop and re-chop the grass clippings. Also, try mowing more often and at a higher blade setting, and just removing a fraction of the grass blade with each mowing.
After dethatching, do any necessary fertilizing, top-dressing and reseeding, as well as applying weed controls. And remember to water well — but it looks like Mother Nature will do that for you!