By Trish Grenfell, UC Master Gardeners of Placer County 

Q: One of my neighbors told me to leave my grass clippings on the lawn, but I feel that it is unsightly and would actually prevent the grass from getting the sunlight it needs to grow. However, it would save me time.  Please advise. 

A: Recycling grass clippings not only is civic-minded (less for the expensive garbage trucks to haul away), but it also can be very beneficial to the lawn. Leaving the cut grass on the lawn can substantially reduce your fertilizer needs—by as much as one-third. When turf is mowed on a regular basis, clippings break down easily, returning nitrogen and other nutrients to the soil. To facilitate this breakdown, the lawn must be mowed often enough to keep the grass clippings short (an inch or less in length) which will decompose rapidly. Using a mower that is made to create mulch also reduces the length of your clippings. Your grass will benefit from more frequent mowing in other ways also. Removing more than one-third of the grass height leaves the grass less resistant to disease and the stress of hot summer weather. You don’t want to scalp your lawn. If you have over fertilized your turf grass with chemicals, you may have to mow more often than once/week—just to adhere to the “no more than one-third” rule. 

Leaving the short grass clippings on the lawn also helps shade the soil during the decomposition process, keeping the roots cooler, and reducing moisture loss just like the regular mulch you put around your plants and shrubs.

Some people are concerned that leaving clippings on the lawn may add to thatch accumulation, but that worry is unfounded. Because short cut grass decomposes rapidly, it does not contribute to thatch. Thatch is a combination of your lawn’s old stems/roots. It accumulates as these plant parts buildup faster than they breakdown. Heavy nitrogen fertilizer applications or overwatering frequently contribute to thatch, because they cause the lawn to grow excessively fast.

If no herbicides have been applied to the grass, homeowners have other uses for those clippings. You can also rake the dried clippings and use them as mulch around trees, shrubs or flowers. Or you can compost them. If you combine clippings with tree leaves, the two sources of yard waste will complement one another in the composting process.