The management of cut grass often results in large volumes of yard waste requiring disposal. Bagging and hauling these clippings off-site represents a significant environmental and labor cost, yet this material is a valuable resource. Grass clippings are rich in nutrients and organic matter, making them beneficial for the lawn and other areas of the landscape. Repurposing this material is a practical way to create a more self-sustaining garden ecosystem and reduce unnecessary waste.
Grasscycling (Leaving Clippings on the Lawn)
The simplest and most recommended use for clippings is grasscycling, or mow and mulch, where the cut grass is left directly on the lawn surface. This method returns essential nutrients to the soil, providing a natural, slow-release fertilizer. Clippings contain approximately 4% nitrogen, 2% potassium, and 1% phosphorus, and their decomposition can supply up to 25% of a lawn’s annual fertilizer requirements.
To ensure the clippings decompose quickly, proper mowing technique is necessary. The “one-third rule” dictates that no more than one-third of the grass blade’s height should be removed in any single mowing session. This results in short, easily-degradable pieces that break down rapidly and do not contribute to thatch buildup.
Maintaining a sharp mower blade is important for successful grasscycling. Dull blades tear the grass, leaving ragged edges that stress the turf, while a clean cut promotes faster healing and quicker decomposition. Mowing when the grass is dry helps the clippings disperse evenly, preventing them from clumping and smothering the grass underneath.
Using Clippings as Garden Mulch and Soil Amendment
When clippings are too long or abundant for the lawn, they are a valuable resource for garden beds and compost piles. Grass is a “green” composting material due to its high nitrogen content, possessing a low Carbon:Nitrogen (C:N) ratio (typically 9:1 to 25:1). This nitrogen-rich material must be balanced with “brown” materials, such as dry leaves, straw, or shredded wood chips, which are high in carbon.
To achieve the optimal decomposition rate (C:N ratio of approximately 25:1 to 35:1), mix about two to three parts of carbon-rich brown material for every one part of green clippings by volume. Failing to add enough carbon can lead to anaerobic conditions. This causes the pile to become slimy, overheat, and produce an unpleasant ammonia odor as excess nitrogen is released.
Clippings also function well as mulch around plants, trees, and shrubs to suppress weeds and conserve soil moisture. Fresh clippings must be applied in a thin layer, ideally no more than one or two inches deep, to prevent matting. If the layer is too thick, the clippings can form a dense, water-repelling mat that blocks oxygen, heats up, and decomposes anaerobically, which can harm plant roots. Dried clippings can be applied in slightly thicker layers.
Safe Disposal and Contamination Concerns
Repurposing grass clippings is generally beneficial, but they should not be used in the garden or compost pile if contamination risks exist. The primary concern is persistent herbicides, such as clopyralid, picloram, and aminopyralid, designed to kill broadleaf weeds in turf. These chemicals do not break down easily and can remain active on the clippings for many months.
If clippings from a treated lawn are used in a garden, the residual herbicide can damage or kill sensitive broadleaf plants like tomatoes, beans, and peppers, even after composting. Avoid using clippings from any lawn recently treated with a “weed and feed” product or a selective herbicide. Wait at least three or four weeks, or two full mowings, before collecting them for reuse.
Clippings heavily contaminated with viable weed seeds, such as crabgrass or clover that have gone to seed, should also be avoided as mulch. When clippings are chemically contaminated or excessively weedy, the material must be safely discarded. Many municipalities require yard waste to be placed in designated organic waste carts, and hazardous chemicals must be taken to a household hazardous waste collection site.