Mulching Grass Clippings Back Into the Lawn

Grass clippings clumped together in front of lawn mower closeup

The Spruce / Steven Merkel

Almost without exception, lawn clippings should always be mulched back into the lawn. The benefits of mulching lawn clippings are too numerous and valuable to ignore. From providing nutrients for the soil to saving significant amounts of time and money, mulching the lawn clippings just makes sense. Similar to mulching leaves into the lawn in the fall, lawn clippings add valuable organic matter to the soil.

How to Mulch

Mulching is best accomplished with a mulching mower, which is just like any other mower with a few modifications. Mulching kits are usually an option available to mowers at the time of purchase, but any mower can easily be retrofitted, as well. Special "mulching" blades with extra cutting surfaces are used in conjunction with added baffling underneath the mower. The output or chute is blocked to trap the clippings underneath the deck. The baffling helps move the clippings around within the mowing chamber and allows them to be cut multiple times and blown down into the surface of the lawn.

Effects on Thatch Growth

A common misconception is that leaving grass clippings on the lawn causes thatch—a dense layer of dead and living grass shoots that forms a mat between the soil and grass blades. But grass clippings do not cause thatch buildup. Clippings consist mostly of water, and the remaining tissue is quickly broken down through microbial activity. Grass clippings may add to an existing thatch problem, but as long as the lawn is mowed regularly and a mulching mower is used, mulching lawn clippings into the lawn will not cause thatch buildup.

However, clumping of grass clippings may occur when you mow under wet or over-grown conditions. Care should be taken to avoid clumping and address it when if it occurs in a thick enough later that can potentially smother the grass. This generally happens only if you mow a lawn that has been allowed to grow too long, or if you mow it when it is wet. Either way, clumping is easily remedied by raking up the grass clumps if they occur.


Think of the effort and resources involved in dealing with lawn clippings. Collecting them with a mower. Dumping into piles or more bags. The removal and disposal. Repeatedly emptying the grass collection bag. The time and labor involved in removing clippings is significant, especially if you consider how beneficial clippings are for the lawn.

Recycling grass clippings back into the lawn can contribute up to 1 pound of a lawn's annual nitrogen requirements. A typical lawn needs up to four pounds of nitrogen annually for healthy growth, so returning the clippings to the lawn can effectively cut out one full fertilizer application, saving time, money, and labor. Clippings are rapidly devoured by worms, beneficial bacteria, and fungus, increasing the diversity and activity of the intricate food web.

The overall goal of an organic or natural-based lawn care program is to achieve 5 percent organic matter in the soil, and most lawns have an organic matter ratio of only 2 to 3 percent. It can take years of topdressing with compost, mulching leaves, and recycling grass clippings to increase the organic matter by even one percent, so there is no better time to start than now.

If the soil biology benefits are not enough to convince you to mulch grass clippings back into the lawn, then maybe the financial rewards will help. A collection system on a lawnmower is far more expensive than a mulching kit. The more times clippings are handled, the more labor is involved. A collection system needs to be emptied, the clippings then need to be put somewhere, either on-site or taken away. If these extra steps do not increase the overall costs of a lawn care service, it certainly contributes to labor, fuel, and machinery maintenance budgets.

If clippings are trucked off-site, where do they go? Tipping fees may be involved if they are taken to recycling facilities. If they are kept on-site and used in a home compost pile, care must be taken with regards to pesticide usage, since chemical pesticides can contaminate compost.

When to Avoid Mulching

  • It is a good idea to collect clippings rather than mulching them back into the lawn if there are an abundance of weeds such as dandelions and crabgrass. Collecting the clippings around the time the weeds go to seed may help reduce the spread of weed seeds throughout the lawn during certain times of the year. 
  • If the lawn has gone un-mowed for over a week due to rain or some other circumstance, it may be wiser to collect the clippings or at the very least mow over the clumps several times to distribute them better.
  • Clippings may not break down effectively in a conventionally maintained lawn if there has been repeated use of chemical pesticides and synthetic fertilizers. For example, insecticides for grub prevention can kill much more than the target pest and can render a lawn almost lifeless. Synthetic fertilizers increase the salts present in the soil which can also reduce soil biology. A lack of microbial activity and earthworms may inhibit the amount of decomposition necessary to break down lawn clippings.