CORVALLIS - In case you've been wondering what to do with your grass clippings, just leave them on the lawn, advises Tom Cook, turf grass specialist at Oregon State University.
Unless you've let the lawn grow excessively long, or the clippings are in thick clumps, grass clippings are a good source of nutrients. Leaving clippings helps save fertilizer costs and thereby prevents ground and surface water contamination.
"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," explained Cook. "And on lawns growing in clay soils, I have produced acceptable quality turf for as long as 12 years without adding any fertilizer at all."
Grass clippings contain up to the equivalent per weight of 3-4 percent nitrogen, .5 percent phosphorus and 2.5-3.5 percent potassium, said Cook.
If you plan to leave the clippings, mow the lawn often.
"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," he said. "I consider mowing more important than fertilizer if clippings are returned via a mulching mower. If clippings are removed, then the only way to keep fertility up is to keep adding more fertilizer."
Your grass should be cut often enough so that not more than one-third of the grass blade is removed at any one time.
Don't leave piles of heavy, wet clippings on the lawn. You need to rake them or the grass underneath may be smothered.
Be sure the mower blade is sharp and cuts, not tears, your grass. A sharp blade will also help chop the clippings into smaller pieces as you mow over the lawn time after time.
A mulching mower works even better, because it is designed to chop up clippings very fine and then deposits them down in the turf canopy.
Despite rumors to the contrary, clippings do not promote thatch build up. Clippings break down quickly, often in a matter of a few weeks.
"Virtually all research conducted with turf has shown that grass clippings do not increase thatch," Cook said. "In most cases, thatch increases as mowing height increases."