Allowing clippings to remain on lawns is recommended for many reasons: eliminating fuel consumption while hauling clippings, not filling landfills, encouraging microbiological activity to promote healthier grass, and recycling nitrogen and other nutrients back into the lawn. Lawn clippings do not add to lawn thatch, Thatch is a brown, spongy material consisting of dead grass stems and roots.
On new lawns with low organic matter, lawn clippings when returned to the lawn, recycle nutrients in an organic, slow-release form that promotes steady grass growth. Clippings provide some of the nutrients needed by the lawn but does not preclude the need for timely fertilization. Lawn soil organic matter levels peak at 30 to 40 years of age and this organic matter supplies one to two pounds of plant available nitrogen per year.
After the first 30 years of a healthy lawn, it could be detrimental to keep fertilizing at the same high rate. Applying 4 pounds of fertilizer per season on top of that supplied by soil organic matter and recycled clippings means the lawn could be receiving 5 to 6 pounds of N yearly. This promotes a lush turf that requires higher amounts of water, is more subject to disease and is less tolerant of heat and drought.
When lawns reach 30 years of age and if clippings continue to be returned to the lawn, nitrogen application rates should be reduced to 2 pounds (two applications per year). This assumes the lawn is mowed at the recommended height and irrigated reasonably. In most circumstances, these practices produce a lawn of acceptable quality to most people and one that is easier to manage under Colorado’s environmental conditions.
Grass clippings break down quickly and encourage the beneficial earthworms and microorganisms that maintain healthy grass and healthy soil. Regular core cultivation (aeration) is the best way to prevent thatch. See fact sheet 7.202, Lawn Care, for more information on thatch management.
Clippings and Nitrogen Fertilization
Nitrogen is the fertilizer nutrient most used by turf. Clippings contain nitrogen and other nutrients. Returning lawn clippings reduces the amount of supplemental nitrogen fertilizer required by lawns but does not eliminate it entirely.