CORVALLIS, Ore. — If your goal is a lush, healthy lawn, keep the grass clippings where they fall. Leaving them in place after mowing nourishes your turf, saves money and helps protect the environment.
“Frequent mowing — about once a week during the growing season — will have a greater impact on turf quality than any other lawn care practice except irrigation in the summer,” said Alec Kowalewski, Oregon State University professor and Grover Family Endowed Sustainable Urban Landscapes Specialist.
Why leave clippings?
Grass clippings are a natural source of nutrients. Unless your lawn has grown excessively tall or clippings form thick clumps, they act like a slow-release fertilizer, returning nitrogen, phosphorus and potassium to the soil.
“Our research has shown that we can cut the fertilizer application rate almost in half when we return clippings with a mulching-type rotary mower,” Kowalewski said. “On lawns growing in clay soils, I’ve produced acceptable quality turf for as long as 12 years without adding any fertilizer at all.”
Clippings contain, by weight, up to 3–4% nitrogen, 0.5% phosphorus and 2.5–3.5% potassium, key nutrients for healthy turf.
Mowing habits matter
If you plan to leave clippings, mow frequently. Cutting about once a week during the growing season helps maintain a dense, vigorous lawn and prevents clippings from clumping.
Your goal should be to remove no more than one-third of the grass blade at a time. A sharp mower blade makes cleaner cuts and chops clippings into smaller pieces that decompose quickly — often in just a few weeks. Most mower manufacturers recommend sharpening blades every 20–25 hours of use.
Mulching mowers work best because they finely chop clippings and deposit them evenly into the turf canopy, where they can break down rapidly.
During wet weather or periods of rapid growth, if you’ve missed a mowing or two, use a bagger to collect heavy clippings. Once the grass is under control, resume mulching.
The truth about thatch
Despite what you may have heard, grass clippings do not cause thatch buildup. Thatch results from certain turfgrass species that spread by stolons — above-ground stems common on golf course greens — not from decomposing clippings.
“Virtually all research conducted with turf has shown that grass clippings do not increase thatch,” Kowalewski said. “In most cases, thatch increases as mowing height increases.”
Benefits beyond the lawn
Leaving clippings on your lawn not only saves fertilizer costs, it also helps reduce the potential for nutrient runoff into waterways. It’s an easy, sustainable practice that benefits your yard and the environment alike.
Previously titled It is best to cut grass often and leave clippings on lawn
