by C.R. Wilson and T. Koski* (3/14)
- One thousand square feet of bluegrass lawn generates about 200 pounds of clippings annually; 75 percent or 150 pounds of this is water.
- Leave clippings on the lawn for healthier grass.
- Clippings break down quickly and encourage beneficial microorganisms and earthworms.
- Nutrients in the clippings are recycled into the lawn, promoting steady grass growth.
- Clippings left on the lawn means no bagging and hauling, saving both human and fuel energy.
Proper lawn care requires regular mowing and produces large quantities of heavy grass clippings. Disposal is inconvenient and expensive and takes up space in landfills. An alternative is to leave clippings on the lawn, which saves labor and promotes a healthy lawn.
Thatch and Clippings
The idea that clippings left on lawns will cause thatch has been disproven. Thatch is a brown, spongy material consisting of dead grass stems and roots.
Excessive thatch is undesirable because it prevents water and air from penetrating to grass roots. A healthy population of microorganisms and earthworms in the soil can digest thatch.
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. When returned to the lawn, clippings recycle nutrients in an organic, slow-release form that promotes steady grass growth. Returning clippings reduces the amount of supplemental nitrogen fertilizer required by lawns but does not eliminate it entirely.
Lawns are most healthy when mowed at 2 1/2 to 3 inches, leaving the clippings on the lawn. To prevent grass from matting over the winter, some people lower the height to 1 1/2 inches for the last mowing in the fall.
Mow frequently enough that no more than one-third of the grass blade is removed. When grass is growing rapidly in the spring, this may mean mowing every five days instead of waiting a full week. This is necessary for two reasons.
First, grass plants undergo less stress when the amount clipped is short compared to the amount remaining. The resulting clippings will be smaller, so they drop into the lawn more easily. Even with mulching mowers that finely chop clippings, mowing more frequently results in less turf stress and allows the mower to work more efficiently.
Second, studies show that it takes less overall time to mow more often and leave clippings on the lawn than it does to mow weekly and bag clippings. If grass becomes excessively long between mowings, it may be necessary to bag or rake clippings to prevent them from matting on top of the lawn.
Various types of mowers are available, each having advantages and disadvantages. From the viewpoint of leaving clippings on the lawn, any mower can do the job if the lawn is mowed frequently before grass becomes too long.
Mulching mowers, a type of rotary mower that chops clippings several times before they fall into the lawn, are a good choice. Bagging mowers may or may not require the bag to be attached. Kits are available to convert some bagging mowers into mulching mowers.
Choice of mower depends on budget, mowing habits and size of lawn. In selecting a mower, consider its ability to return grass clippings to the lawn.
Many municipalities are getting out the message to “take the waste out of yard waste.” Yard waste makes up 20 percent of materials sent to landfills annually, yet 100 percent of it can be recycled. Less yard waste means less trash hauling for municipalities. Savings in labor, fuel and other costs can be substantial.
Clippings as Compost or Mulch
If clippings are too long to leave on the lawn, there are at least two alternatives for recycling them: composting and mulching.
Grass clippings contain nitrogen and can be a valuable addition to compost. Compost is useful for improving Colorado’s heavy clay or light sandy soils. See 7.212, Composting Yard Waste, for information on how to compost.
Clippings also can be recycled as mulch in the garden. Mulching reduces weeds, modifies soil temperature, and retains moisture. Mulch maintains good soil structure by reducing the force of rain droplets. It minimizes erosion by protecting the soil surface. When using clippings as a mulch, layers deeper than 2 inches will rot and produce a foul smell. Scatter and allow the first thin layer to dry. Later, add more clippings to produce a 4- to 6-inch deep mulch.
Do not mulch with clippings from a lawn that has been treated with a weed control product within the last two weeks. The herbicide on the clippings can harm desirable bedding and garden plants. These clippings are best left on the lawn where the clippings and herbicide are broken down naturally by soil microbes and earthworms. Always read and follow the label on all pesticides, including herbicides.
*C.R. Wilson, Colorado State University Extension horticulture agent, Denver County; and T. Koski, Extension turfgrass specialist, horticulture and landscape architecture. 4/95. Revised 3/14.
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