How Long Does it Take for Grass Clippings to Decompose?

Have you ever mowed your lawn after a nice summer rain, only to your dismay that it looks like you farmed your yard with rows upon rows of freshly cut, damp grass piled inches high?

You may have wondered, what am I to do now? Will that grass degrade by itself?

This article will give you information on how to make those clippings decompose faster, why those clippings improve your lawn, and how to use them as mulch and compost.

How do you Make Grass Clippings Decompose Faster?

The best way to make your grass clipping decompose faster is to mow regularly. Make sure your mower blades are sharp. Avoid cutting when there is moisture in the grass. However, should those troublesome “farmers” rows appear, you either: re-mow and disperse the clippings or rake and gather for another use.

Set the height of your mower so that you are only cutting the top 1/3 part of the grass height.

  • For cool-season grasses, set your mower at 2-1/2 to 3-1/2 inches.
  • For warm-season grasses, use a setting from 1-1/2 to 2-1/2 inches. 

Mowing your grass tall encourages root growth. This reduces the need for watering and creates a lusher lawn. It also helps to prevent weeds from growing or getting established. Mowing your grass often will make the clippings decompose faster.

Why Do Grass Clippings Improve Your Lawn?

Grass clippings provide a natural fertilizer as they break down into the lawn soil, as they contain 4% Nitrogen, 2% Potassium, and 1% Phosphorus.  A fancy word for leaving the grass clippings on your lawn after you have mowed is called “grasscycling.” There is a great advantage to this process.

If you keep your clippings short, grasscycling is the most natural and efficient method for your clippings to decompose. Warm weather and deep watering help this process happen quickly. Water your lawn once per week for lengthy periods to encourage a good decomposition.

Thick thatch can slow the process of grass clipping decomposition. Thatch is a combination of grass roots, runners, and stems that form a barrier between the growing grass and the soil. Grass clippings do not add to the thatch, but dethatching your lawn should improve the breakdown of the clippings as they add more nutrients. This is why grass clippings strengthen your lawn.

Add a Thin Layer of Grass Clippings

Grass clippings make excellent mulch material.  Place a thin layer of dry grass clippings (about 1-2″) in your garden and flower beds. This will help prevent weed growth, retain moisture and reduce erosion. The grass will decompose into organic matter and plant nutrients in the soil. Reapply as needed.

Feel free to add other organic matter such as dried leaves or wood chips to your mulch. Let the clippings decompose before adding additional clippings. Too thick of clippings start to rot and become moldy and stinky.

Will Grass Clipping Turn into Dirt?

Will Grass Clipping Turn Into Dirt

Composting your grass clippings is an excellent way to break them down into organic soil. Because grass clippings are high in nitrogen, you need to do a 1:1 or 1:2 ratio with brown organic matter (carbon) such as dry leaves, straw, and hay. You may also add any vegetable components, eggshells, and coffee grounds.

The combination of nitrogen and carbon will begin to heat quickly and start the process of decomposition. It is important to turn and mix your compost weekly to ensure thorough composting so smell and decay do not linger. Once decomposed, you have organic soil or dirt.

Is Rotted Grass a Good Compost?

It is fine to add rotted grass to the compost mixture. Just thoroughly mix in and turn regularly.

When not to Use Your Grass Clippings

If your lawn has a disease or fungus, it is best not to use the grass clippings for anything. Using them will only promote further lawn or garden illness. Remove the clippings and throw them away or burn them. Most landfills have banned grass clippings in many states. Check with your local landfill before putting out for trash.

In addition, if you are using herbicides and/or weed killers on your lawn, be aware that the chemical will remain on the clippings. Depending on the chemical or brand, your clippings should be good to use in 3-4 weeks; after the chemical has evaporated.

How Long Does It Take for Grass Clipping to Decompose?

Grass clippings on the lawn

As you have read, there are several ways to utilize your grass clippings that will provide nutrients, protection and allow the waste to degrade naturally back into the soil. Here is exactly how long this will take, depending on which route you use:

  • Grass clippings on the lawn: Full decomposition in 3-4 weeks
  • Grass clippings for mulch (1-2″) at a time: Full decomposition 1-3 months
  • Grass clippings in compost: Full decomposition 1-4 months or longer if not properly aerated

Whether you choose to do grasscycling, mulching, or composting, you can bet that you will have a happy, healthier lawn and garden by utilizing those clippings!


Author: Matt Hagens

Hi, I’m Matt the owner of Obsessed Lawn. I love to be outside working on my lawn, planning my next project. I created this website to help people like you find the best products for yard care and great advice. Learn more about me and find me on Facebook.