How To Compost Grass Clippings

Got a stinky, slimy pile of grass clippings? Here’s how to compost grass clippings without the smelly mess.

While grass clippings can be a valuable addition to your compost pile, grasscycling is better for your lawn – and less work – than collecting and composting grass clippings.

Grasscycling is simply recycling your clippings by leaving them on your lawn to decompose naturally. If you need to collect them, composting grass clippings is a better alternative to sending them to the landfill.

When is it a good idea to bag clippings? It’s helpful to remove clippings when your lawn must be mowed and is wet or excessively tall – leaving grass clumps. You can also quickly clean a lawn full of leaves/debris by mowing with your grass catcher.

How NOT To Compost Grass Clippings

I used to work as the gardener for a large estate. The owner insisted on collecting ALL of the grass clippings, and we generated a lot of them. There were concrete bins near our shop that were stockpiled with mulch and topsoil. Instead of hauling the clippings and spreading them in one of the fields, I decided to “compost” the grass clippings in the spare bin. We accumulated a large pile of grass clippings that quickly turned into a stinky, slimy mess.

It rained a lot that summer so the pile stayed wet. We turned it weekly with the skid steer while continuing to add more grass clippings, garden trimmings and some soil. Our mountain of lawn cuttings remained a foul-smelling mess.

What did we do wrong? (We should have googled how to compost.)

A pile of grass clippings has a very high moisture content and tends to form a compact mat that restricts air movement. This was causing our heap to compost anaerobically – emitting a foul smell. There was too much nitrogen and moisture and not enough bulk material – leaves, wood chips, hedge clippings, straw, etc.

How to compost grass clipping with man turning compost with shovel

Grass clippings are a great addition to a compost pile, they are rich in nitrogen that the microbial population uses as they decompose the organic matter. Dry leaves, wood chips or straws need to be mixed in a 1:1 or 2:1 ratio with clippings to produce good compost and reduce odors.

How to Compost Grass Clippings

Composting grass clippings in wheel borrow

If you bag your lawn cuttings, you will be collecting them faster than they can compost. The best way to handle a continuous supply of grass clippings is to have multiple compost piles at different stages of decomposition. You will then have a place to dump fresh clippings while moving materials that are starting to decompose into your other piles.

Composting tips, compost bin

Keys to a successful compost pile:

  1. Everything organic has a given ratio of carbon to nitrogen (C: N) in its tissues. Compost microbes use carbon for energy and nitrogen to build proteins and grow. The ideal C: N ratio for these microbes is 30:1. Lawn clippings alone have a 15:1 ratio.
  2. Shredded materials – leaves, bark and chipped wood – will compost easily and are important to use with your lawn clippings because they add bulk that creates air space and increases the ratio of carbon to nitrogen.
  3. Your pile needs to be moist – not wet. Dry organic matter decomposes slowly, a wet pile will lead to anaerobic conditions.
  4. Microbes need nitrogen for their own metabolism and growth. Your grass clippings are rich in nitrogen and enhance decomposition when mixed properly with other yard wastes. For example, two parts leaves to one part clippings.
  5. Speed up the composting process by mixing your pile at least once a month.
  6. It usually takes 3 months to make good compost. Your compost will be ready to use when it is dark, crumbly and smells earthy.
Finished garden compost ready to use.

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Composting Tips

This is a really good step-by-step video:

Drums and Tumblers

Compost tumblers or a compost drum will make compost fast. They also save space and contain odors, which is perfect for small properties. These are easy for the handy DIYer to make (like the one pictured on the left) or purchased from a retailer. There are several styles to choose from.

Compost drum
  1. Spread out your grass clippings to let them dry out before adding them to your compost pile.
  2. Don’t use lawn clippings treated with an herbicide (weed killer) for at least two to three weeks after the application. Do not use grass clippings from Lawns treated with Clopyralid – sold as Curtail or Confront – this chemical does not break down rapidly during the composting process.
  3. Compost tumblers or a compost drum will make compost fast. They also save space and contain odors, which is perfect for small properties.
  4. A common belief is that lime needs to be added…you don’t need to add lime to your compost pile.
  5. Cover your pile with a tarp during wet weather to avoid excessive wetness. Uncover it after heavy rains to let it breathe
  6. Compost is not a fertilizer, it contains a tiny amount of plant nutrients. However, it improves soils by adding organic matter.
  7. Composting with Worms A new 13-page booklet by the Oregon State University Extension Service gives detailed instructions on how to build a worm compost bin and how to compost with worms in a process called “vermicomposting.”

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