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Extension > Garden > SULIS > Maintenance > Sustainable Lawncare Information Series > Managing Grass Clippings

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Managing Grass Clippings

Grass clippings will always be a part of lawn care. Because lawns grow at different rates depending on environmental conditions and management practices, it is important to tailor mowing, fertilizing, and watering to meet plant needs, yet avoid excessive growth. Grass clippings an inch or less in length filter down to the soil surface and decompose relatively quickly. Longer clippings have a tendency to remain on the lawn surface where they appear unsightly and can shade or smother grass beneath. Long clippings need to be removed to avoid both unsightliness and lawn damage (Fig.8.7).

Figure 8.7. Excessive clippings left on the lawn surface are unattractive and can cause damage.

Bagging clippings did not become commonplace until the 1950s when bagging attachments were designed for rotary motors. In nearly every instance, proper lawn care can greatly reduce or eliminate the need to collect clippings. In fact, clippings are a valuable source of nutrients. University of Minnesota soil test recommendations call for less nitrogen fertilizer if clippings are returned to the lawn. Also, the addition of organic matter in the form of clippings may help to improve the status of your soil if it is sandy, heavy clay, or low in organic matter.

Contrary to popular belief, returning clippings to the lawn does not contribute to increased thatch formation. Thatch is a layer of undecomposed organic matter that builds up between the soil surface and the actively growing green vegetation (Fig. 8.8). A thatch layer will develop if organic matter is produced faster than it is decomposed by microorganisms.

Figure 8.8. Soil core showing location of thatch layer below turfgrass canopy.

The major factors contributing to thatch development are vigorous grass varieties, excessive nitrogen fertilization, infrequent mowing, and low soil oxygen levels (such as found in compacted or water logged soils). Clippings are composed primarily of easily degradable compounds which break down rapidly and do not accumulate. Long clippings may contain wiry stem material that is slower to decompose, but are still not significant contributors to thatch buildup.

Table 8.1. Are There Times When I Should Pick Up Clippings?

While leaving clippings on the lawn is recommended, certain instances make the practice inadvisable. Following are some exceptions to the rule:

  • If the lawn is heavily infested with certain leaf diseases (such as leaf spot, rust or dollar spot), removing clippings may help reduce disease severity.
  • If the lawn must be mowed when wet or the grass has become too tall, clippings can mat together and smother the grass.
  • If your mower is unsafe to operate without a bagging attachment, the bag must be left in place.
  • If clippings land in curb and gutter area, especially near storm drains, sweep up to avoid having them get into storm drains, be carried to nearby water resources and negatively impact water quality (Fig. 8.9).

Figure 8.9. Remove grass clippings from curb and gutter, especially near storm drains.

Using clippings as a garden mulch or composting them are two good alternative disposal methods (Fig. 8.10).

Figure 8.10. Grass clippings used as mulch around annual bedding plants.

Mulching helps reduce weeds, conserve moisture, and modify soil temperatures. However, do not apply more than 1 or 2 inches of grass clippings as mulch at one time.

Wet grass clippings can mat down and reduce oxygen and moisture from getting down into the soil. When oxygen is limited, anaerobic decomposition of the clippings may take place, leading to the production of offensive odors.

In general, do not use grass clippings as mulch if the lawn was recently treated with an herbicide for dandelions or other broadleaf weeds. Consult herbicide product label for any concerns related to using clippings as mulch.

Composting involves mixing grass clippings and other plant materials with a small amount of soil containing microorganisms which decompose organic matter. Grass clippings are excellent additions to a compost pile because of their high nitrogen content. However, they should not be the only compost component and should be interspersed among other compost ingredients to avoid packing together (Fig. 8.11).

Figure 8.11. Compost bin structures containing grass clippings.

As with mulches, a thick layer of grass clippings in a compost pile will lead to bad odors from anaerobic decomposition. Mix them with dry materials such as leaves or straw. Clippings can be composted in the backyard or hauled to municipal composting sites. For more information on compost and composting see:

Composting and Mulching – A Guide to Managing Organic Yard Wastes

Selecting Commercial Compost

Proceed to Mowers and Mower Safety – Choosing a Mower

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