Recycling Turfgrass Clippings

Recycling grass clippings also returns valuable nutrients back to your lawn. Research at Penn State has shown that over a three-year period, leaf clippings from Kentucky bluegrass contained 46 to 59 percent of the nitrogen (N) applied as fertilizer. When clippings are returned to the lawn, you can reduce fertilizer applications.

Several tools and management practices can be used to make the recycling process more efficient. A few of the more effective practices are described below.

Mowing Practices

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 sometimes not frequent enough, especially during the peak period of leaf growth in the spring. The lawn should be mowed at the suggested height of cut for the predominant turfgrass species present (Table 1).

Table 1. Suggested mowing heights for cool-season turfgrass species used in Pennsylvania lawns.

Some people are concerned that returning clippings to the lawn may result in thatch accumulation. Thatch is the tightly intermingled layer of partially decomposed stems and roots that develops between actively growing green vegetation and the soil surface. Because turf clippings are composed mostly of leaf tissue that decomposes rapidly, they do not contribute to thatch.

If the soil pH near the surface is low, populations of microorganisms that decompose the clippings may be reduced. To ensure that adequate microbial decomposition occurs, maintain the soil 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 extension office for a nominal fee.

Mulching Mowers

Mulching mowers are rotary mowers designed to keep the clippings circulating under the mower deck so the grass blades will be chopped into finer pieces. This hastens clipping decomposition and reduces the amount of residue on the lawn. Some mowers have special features that facilitate mulching, such as multiple rippled blades and dome-shaped decks that allow better circulation of clippings. Lawn mower manufacturers also offer mulching features that block discharge 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. Excessive applications of soluble nitrogen fertilizer in early to mid-spring will produce a large flush of growth. Fertilizers used for home lawns typically contain at least 33 percent slow-release nitrogen. Nitrogen fertilizer should be applied in relatively small amounts to lawns (usually no greater than 1.0 pound of nitrogen per 1,000 square feet) in two to three applications over the course of a growing season. The best times of year to fertilize lawns in most areas of Pennsylvania are spring (April or May) and late summer (early to mid-September). Suggested annual amounts of nitrogen fertilizer for cool-season turfgrasses grown in Pennsylvania are listed in Table 2. The amounts of other nutrients (phosphorus and potassium) and lime to apply should be based on soil test recommendations.

Table 2. Suggested nitrogen fertilizer amounts for cool-season turfgrass species used in Pennsylvania.

*Annual amounts of nitrogen in the low range are usually adequate for older lawns (more than 10 years old) growing in inherently fertile soils. High ranges are sometimes used for newly established lawns grown in infertile soils.

Irrigation

Excessive irrigation can increase leaf growth of turfgrasses and mowing frequency. This practice will eventually weaken the turf and may cause disease problems. In dry periods, a sufficient amount of water should be applied to ensure that the entire root system will be moistened. If water runs off the lawn before soaking into the soil, turn off the sprinkler, allow the water to soak in, and continue irrigation. Excess water saturates the soil and results in poor root development.

Special Considerations

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