Grass clippings can fertilize lawns

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Last Updated: 
May 1, 2007

CORVALLIS - People who use grass clippings to mulch shrubs and flowers are simply "robbing Peter to pay Paul," says Tom Cook, turf grass specialist at Oregon State University.

"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," said Cook. "And on climax bentgrass lawns growing in clay soils, we have produced acceptable quality turf for as long as 12 years without adding any fertilizer at all."

Grass clippings are a good source of nutrients for your lawn, with up to the equivalent per weight of 3 to 4 percent nitrogen, .5 percent phosphorus and 2.5 to 3.5 percent potassium.

However, if you plan to leave the clippings, mow the lawn frequently. Your grass should be cut often enough so that not more than one-third of the grass blade is removed at any one time. That means mowing about once a week during the growing season, according to Cook.

Light, frequent mowing will not leave piles of heavy, wet clippings on the lawn. If the lawn is too high, you will need to rake clippings or the grass underneath may be smothered.

And be sure to set the mower at the optimum height. Mowing grass too short can reduce its density and increase the invasion of other grasses and weeds.

On the other hand, several problems may develop when grasses are cut above their optimum height, according to Cook. For example, Kentucky bluegrass is more susceptible to stripe rust and perennial ryegrass tends to shred if mowed above two inches. Colonial bentgrass will develop high crowns, and looked scalped and brown when mowed at two inches or higher.

Despite rumors to the contrary, clippings do not promote thatch build up. Clippings break down quickly, often in a matter of a few weeks. However, thatch may increase as mowing height increases.

For more information about "Maintaining a Healthy Lawn in Western Oregon," EC 1521, visit our on-line catalog. Our publications and multimedia catalog at: http://extension.oregonstate.edu/catalog/ shows which publications are available on the Web and which can be ordered as printed publications.

Author: Peg Herring
Source: Tom Cook