Managing Your 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 above the lawn where they appear unsightly and can shade or smother grass beneath. Long clippings need to be removed to avoid both unsightliness and lawn 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 or low in organic matter.

Contrary to popular belief, returning clippings to the lawn does not normally 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. A thatch layer will develop if organic matter is produced faster than it is decomposed by microorganisms. The major factors contributing to thatch development are vigorous grass varieties, excessive nitrogen fertilization, infrequent mowing, and low soil oxygen levels. Small 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 slow to decompose.

Alternatives to Leaving Clippings

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

If the lawn is heavily infested with certain leaf diseases, removing clippings may help reduce disease severity. If the lawn must be mowed when wet, clippings can mat together and smother the grass. If the grass has become too tall, clippings can mat together and smother the grass.

When clippings must be collected, using them as mulch in the garden or composting them are two good alternative disposal methods. Grass clippings can provide an effective mulch around garden plants. Mulching helps reduce weeds, conserve moisture, and modify soil temperatures. However, do not apply more than one or two inches of grass clippings as a mulch at one time. Wet grass clippings can mat down and prevent 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. Do not use grassclippings as mulch if the lawn was recently treated with an herbicide for dandelions or other broadleaf types of weeds. If clippings are to be used as a mulch, then wait until its been mowed at least twice.

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. 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.

Source:
“Managing Grass Clippings,” University of Minnesota, Sustainable Urban Landscape Information Series: http://www.sustland.umn.edu/maint/mowing.htm[accessed on May 6, 2008].