Many lawn mowers are capable of mulching grass clippings or collecting clippings in bags. Although some people worry that mulched grass clippings contribute to thatch or look unsightly, leaving mulched clippings on the grass is almost always better for your lawn than bagging grass clippings.
Leaving clippings on your grass saves time when you mow and returns essential nutrients to the grass, cutting fertilizer requirements by 25 percent. Mulching grass clippings also saves money because you don't have to purchase trash bags or buy as much fertilizer. It also saves space in landfills. Mulching mowers should distribute clippings evenly, not in clumps, so clippings won't look unsightly, either.
Many people believe leaving grass clippings on the lawn encourages thatch, a layer of roots, stems and other organic material that builds up between the grass and soil. Too much thatch causes problems because it blocks sunlight and moisture from the soil. Grass clippings do not cause thatch, however, because they are 80 to 85 percent water and break down very quickly.
If you let your grass grow too long and need to cut an inch or more off the lawn, consider bagging or removing the clippings. However, cutting the grass gradually back down to its desired height over a period of a week or two is healthier than cutting an inch or more; you should never remove more than 1/3 of the leaf blade at a time. You should also bag clippings if you already have a layer of thatch of 1/2 inch or more because grass clippings may increase thatch once it is present. In addition, don't mulch clippings if your grass is diseased because it may spread the disease.
Even if you remove grass clippings from your lawn, you don't need to throw them away. In fact, many areas do not permit homeowners to throw away grass clippings. Instead, use grass clippings or leaves as mulch. Allow grass clippings to dry before mulching, and apply a thin layer. Alternately, decompose clippings and other yard waste in a compost pile. However, don't compost or mulch grass clippings if you've recently treated your lawn with a pesticide or herbicide.