Grass Cuttings: Bag or Not to Bag?

Many homeowners struggle with the decision of whether or not to bag grass clippings. On one hand, bagging grass clippings keeps your lawn looking neat and clean. This is tempting, but in most situations the right answer is to leave the clippings on the lawn. Bagging your grass clippings not only adds work for you, it creates waste and removes what could be a vital element to a healthy and thriving lawn.

When you bag your grass clippings, you must either compost them or trash them, which makes the clippings waste material. This is a problem because as grass clippings decompose in landfills, the nutrients they contain are no longer beneficial. Instead they contribute to contamination of groundwater and to landfill leachate. According to the University of Idaho, grass clippings can comprise up to 20 percent of the solid waste that is sent to landfills on a yearly basis, so trashing your grass clippings also reduces valuable landfill space.

Grass clippings contain about 4 percent nitrogen, 0.5 percent phosphorus and 2 percent potassium, reports the University of Idaho. They also contain trace elements of other important plant nutrients. Research studying the nutrients in grass clippings has shown that by leaving them on your lawn, you can supply 25 percent of the lawn’s total nutritional needs. When you leave the grass clippings on your lawn, you’re giving your grass a natural source of nitrogen. As they decompose, the clippings filter down to the soil and decompose within a few weeks, feeding not only your grass, but also soil organisms. Grass clippings left on the lawn also add nutrients and organic material to the soil, which helps improve its structure and increases its fertility.

Many people believe that leaving grass clippings on your lawn will contribute to the growth of thatch, which is a layer of living and dead organic material that develops between the soil and the base of the plant. However, the plant parts that contribute to thatch are roots, rhizomes and grass stolons. Grass clippings do not contribute to thatch because they don’t contain a lot of lignin and decompose rapidly. Thatch is usually caused by overfertilizing and overwatering.

There are some situations where bagging your grass clippings are better than leaving them on your lawn. If there are signs of disease, such as slimy growths or discoloration, pick up the clippings to avoid spreading the disease. If the grass clippings are too long to filter down to the soil rapidly, you may also want to bag them to avoid unattractive clumps and tracking the clippings indoors. In this case, bag up the clippings and apply a 1-inch-thick layer of clippings around ornamental plants. You can also incorporate grass clippings directly into garden soil working about 2 to 3 inches of clippings to a soil depth of 6 to 12 inches. You can also add grass clippings to your compost. Compost piles heat soon after the grass clippings are added, which results in higher pile temperatures that kill off weed seeds and disease. However, grass clippings should make up no more than one-half of the volume of your compost pile. Turn the clippings into the pile within 24 hours of adding them.