What to do with grass clippings: lawn, mulch, or compost

The best thing to do with grass clippings is to leave them on the lawn. University of Missouri Extension says returned clippings supply up to 25 percent of a lawn’s fertilizer needs, and research shows they don’t cause thatch. Mow often enough to remove no more than one-third of the blade at a time, so clippings stay short. Extra clippings make good mulch in 1-inch layers, or a nitrogen-rich compost ingredient. If the lawn was sprayed with herbicide, leave clippings on the lawn for two or three mowings before you collect them.

Lawn healthy and mowed often? Leave the clippings where they fall. Need mulch for the vegetable garden? Dry the clippings and spread them 1 inch at a time. Have a compost pile? Mix clippings with dry leaves or straw. Lawn just treated with weed killer? Leave clippings on the lawn for two or three mowings, and keep them out of the garden. Thatch thicker than half an inch? Dethatch before you start leaving clippings.

Grass clippings are a valuable resource. Whether left on the lawn, composted, or used as mulch, they provide essential nutrients, improve soil health, and reduce waste.

Grass clippings contain about 4 percent nitrogen, 2 percent potassium, and 1 percent phosphorus, according to University of Missouri Extension. Returned to the lawn, they can supply up to 25 percent of its fertilizer needs. Managed well, clippings recycle nutrients, help hold soil moisture, and cut fertilizer use.

Options for handling grass clippings from your lawn

You have several options for handling lawn clippings, depending on your lawn care goals and available space:

Leave them on the lawn

Leaving short grass clippings on the lawn lets them break down fast and return nutrients to the soil. Any type of mower works, according to University of Idaho Extension. For the best results:

• Mow frequently so the clippings are under an inch long
• Cut no more than one-third of the grass height at a time
• Mow when the grass is dry to prevent clumping
• Use a mulching mower to break clippings into smaller pieces, though a regular rotary mower with the catcher removed also works

Use them as mulch

Grass clippings can be used as mulch in flower beds, vegetable gardens, and strawberry patches. Spread a layer around plants in garden beds to retain moisture, suppress weeds, and enrich the soil. University of Missouri Extension suggests adding a 1-inch layer at a time. When using clippings as mulch:

• Let the clippings dry before spreading
• Add about 1 inch at a time to avoid matting, with a total depth of no more than 3 to 4 inches
• Don’t use clippings from a lawn treated with weed killer as mulch

Compost them

Grass clippings make excellent compost material when mixed with dry leaves, straw, or other brown materials. To compost clippings effectively:

• Mix clippings with carbon-rich materials to prevent odor
• Turn the pile regularly to speed up decomposition
• After an herbicide treatment, return clippings to the lawn for two or three mowings before you compost them
• Don’t use clippings from other people’s lawns unless you know what was sprayed

Incorporate them into soil

Clippings can be worked directly into garden soil to boost organic matter. To use them effectively:

• Mix small amounts into the topsoil
• Avoid overloading any one area
• Combine with other organic materials for balance
• Don’t dig in clippings from a lawn treated with weed killer

Bag and remove excess clippings

If clippings are too long or clump together, and you don’t have a compost heap available at home, collect and dispose of them through a municipal yard waste program or composting facility.

Avoiding common issues

Common issues with lawn clippings include thatch buildup, clumping, smothering, and spread of weeds.

Thatch buildup

Some worry that leaving clippings on the lawn causes thatch. But clippings are 80 to 85 percent water and break down much faster than other grass parts. Research at Missouri and other universities shows clippings don’t add to thatch on cool- or warm-season grasses. Before you start leaving clippings, make sure any existing thatch layer is no more than 1/2 inch thick.

To prevent buildup:

• Keep mowing blades sharp for clean cuts
• Mow at the right height to produce short clippings
• Rake or spread out thick clumps of clippings

Clumping and smothering

Thick clumps of grass can block sunlight and airflow, leading to uneven lawn growth.

Prevent clumping by:

• Mowing frequently to keep clippings small
• Avoiding mowing when grass is wet
• Using a mower with a mulching feature

Weed spread

Grass clippings can contain weed seeds. Seeds can come from weeds in the lawn, the surrounding landscape, or from neighboring properties.

To prevent spreading weeds:

• Mow before weeds go to seed
• Use clippings only from a well-maintained lawn
• Compost thoroughly to kill weed seeds

Grass clippings and herbicides

Herbicides used on home lawns can last in the soil from less than a month up to 12 months, depending on the product, per University of Missouri Extension. Kansas State Extension notes that herbicide in grass clippings is the most common cause of contaminated garden mulch and compost. K-State recommends not collecting clippings for the first month after an application. If you get clippings from a neighbor, ask what they sprayed and when.

Grass clippings FAQ

Should I leave grass clippings on my lawn?

Yes, in most cases. They return nutrients and can supply up to 25 percent of a lawn’s fertilizer needs. Mow often so the clippings stay short.

Do grass clippings cause thatch?

No. Research at the University of Missouri and other universities shows clippings don’t add to thatch.

Can I use grass clippings as mulch in my vegetable garden?

Yes, if the lawn wasn’t treated with weed killer. Let them dry and add about 1 inch at a time.

How long after spraying weed killer can I use grass clippings?

Leave clippings on the lawn for at least two or three mowings, or about a month, before you compost them or use them in the garden.