Composting Fertilized Grass

Leaving grass clippings on the lawn promotes self-fertilization.
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In an effort to reduce the amount of organic waste heading to the landfill each week, many communities are eliminating residents’ ability to place yard waste such as grass clippings into the regular trash pickup. Composting grass clippings seems like an effective alternative for managing yard waste, but questions arise about whether this is a practical or safe solution, especially if the lawn has been fertilized.

What is Compost?

Nutrient-rich compost comes from a collection of decomposed organic materials such as fruit and vegetable peels, dried leaves and fresh grass clippings. The right balance of carbon and nitrogen from these materials, combined with the right amount of water, promotes a healthy environment for microbes, worms and other insects. When these organisms move in, they begin the process of decomposition. Depending on temperature, moisture and the contents, a 3-feet by 3-feet by 3-feet compost pile takes two to 12 months to turn into rich brown, crumbly, usable compost, ready to fertilize a garden or lawn naturally. (See Reference 3)


Although raking and collecting your grass clippings can be hard work, placing the clippings into the compost has a couple of advantages. Most compost pile recipes call for nitrogen-heavy fertilizer to jump-start the composting process. Adding fertilized grass clippings to the pile may eliminate the need for additional fertilizer. In addition, the final compost maintains many of the nutrients found in the original ingredients, including the nutrients from the fertilizer used on the grass.


Even though the addition of fertilized grass clippings may boost the nutrients in the final compost, it also has a few disadvantages. Collecting the grass clippings is a lot of extra work. Additionally, if the raked piles of clippings aren’t collected immediately, rain and wind transport those clippings from your yard to local waterways. The fertilizer from the clippings disrupts the balanced ecosystem in ponds, streams and lakes, promoting harmful algal blooms which, according to the Centers for Disease Control, "can deplete the oxygen and block the sunlight that other organisms need to live, and some can produce toxins that are harmful to the health of the environment, plants, animals, and people." (See Reference 1)

Better Alternative

Instead of collecting the fertilized grass clippings, let them lie among the freshly cut grass. The U.S. Environmental Protection Agency explains that “Natural decomposition will usually take care of grass clippings if they are simply left in place.” (See Reference 2) Because the clippings are spread through the lawn and trapped under the growing blades of grass, wind and water won't carry them to local waterways. As the clippings decompose naturally, they replenish the lawn with nutrients.

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