Recycling Turfgrass Clippings

Grass clippings and other yard debris represent a large percentage of solid waste deposited in landfills. An analysis of the composition of residential waste in Cincinnati, Ohio showed that yard debris (leaves, prunings, and grass clippings) accounted for nearly 20% of the total. A study in Plano, Texas (population 80,000) revealed that over 700 tons of grass clippings were collected and disposed of in landfills each week. In addition to the demand for landfill space, collection and disposal of this waste material is expensive.

The obvious solution to the clipping disposal problem is recycling. This can be accomplished easily by returning the clippings to the lawn. If performed correctly, returning grass clippings should not detract from the appearance of the lawn or cause an accumulation of thatch. In fact, this practice will reduce the labor involved in bagging and return essential nutrients to the soil. Research at Penn State has shown that over a three year period, the leaf clippings from Kentucky bluegrass contained between 46 to 59% of nitrogen (N) applied as fertilizer. When clippings are returned, a substantial amount of N and other nutrients can be used by the turf, thus, significantly reducing fertilizer requirements.

There are several tools and management practices that can be used to make the recycling process more efficient. A few of the more effective practices follow:

Mowing practices

In order for clippings to break down rapidly, the lawn should be mowed frequently enough so that large amounts of leaf residue do not remain on the surface of the turf. Weekly mowing is often not frequent enough, especially during the peak period of leaf growth in spring. As a rule of thumb, no more than 1/3 of the leaf tissue should be removed during the mowing operation. The turf should be mowed at the suggested height of cut for the predominant species present (Table 1.).

There is some concern that returning clippings to the lawn may result in the accumulation of thatch. Thatch is the tightly intermingled layer of partially decomposed stems and roots which develops between actively growing green vegetation and the soil surface. Turf clippings are composed mostly of leaf tissue that decomposes rapidly, thus they do not contribute to thatch. If the soil pH near the soil surface is low, populations of microorganisms which decompose the clippings may be reduced. To insure that adequate microbial decomposition occurs, make sure the soil is maintained at a pH between 6.3 and 7.0. Soil pH can be determined through a soil test. Soil test kits are available from your county cooperative extension office.

Mulching mowers

Mulching mowers are rotary mowers that are designed to keep the clippings circulating under the mower deck so that the blades will be chopped into finer pieces. This will ultimately hasten clipping decomposition and reduce the amount of residue on the lawn. Whereas some of the newer mowers have special features that facilitate the mulching (e.g. multiple rippled blades and dome-shaped decks that allow better circulation of clippings), some lawn mower manufacturers are offering mulching ‘kits’ which are essentially plates that block discharge shoots and force the clippings back through the blades.

Fertilization

The amount and type of fertilizer used as well as the time of year the fertilizer is applied will greatly influence the rate of leaf growth of turfgrasses. Heavy applications of soluble N fertilizer in early to mid-spring will produce a large flush of growth. N-sources used for home lawns should contain at least 33% of the N as water insoluble nitrogen (WIN). N fertilizer should be applied in relatively small amounts (usually no greater than 1.5 lb N/1000 ft2) in 2 to 3 applications over the course of a growing season. The suggested times of year to fertilize turf in most areas of Pennsylvania are mid to late May, early to mid September, and in late fall before the ground freezes. Suggested N fertilizer rates for cool-season turfgrasses grown in Pennsylvania are listed in Table 3.

Irrigation

Excessive irrigation can increase leaf growth of turfgrasses and increase your mowing frequency. Eventually, this practice will weaken the turf and cause disease problems. Watering deeply (until the soil surrounding the entire root system is moist) only when turfgrasses show initial signs of wilt is one approach to avoiding excessive irrigation. If water runs off the lawn before soaking into the soil, turn off the sprinkler, allow the water to soak in, and continue irrigation. Frequent light watering encourages shallow rooting and germination of weed seeds.

Special Considerations

Occasionally, periods of prolonged rainfall make mowing difficult or impossible. Is such cases, the turf becomes overgrown and large clumps of grass may remain on the lawn following mowing. The clumps of grass can be remowed after drying to facilitate dispersal or can be removed, air-dried, and used as mulch around trees, shrubs, or gardens. If the turf has been treated with broadleaf herbicides (2,4-D, MCPP, Dicamba, etc.) prior to mowing, do not place clippings around trees, shrubs, or garden pants.