The easiest way to manage grass clippings is grasscycling, (just leave grass clippings on the lawn). However, if you prefer to remove grass after mowing, you can compost grass clippings, if you are willing to actively manage your composting process.
Freshly mowed grass has a high moisture content, and higher nitrogen content than many other materials. The moisture can cause the grass to mat down and clump up, resulting in anaerobic (no oxygen) pockets. This clumping effect, combined with the relatively high nitrogen content of fresh grass clippings and improper composting methods may result in odor problems. However, adding this material can help heat up your compost process and, therefore, adding grass to the compost bin may be desirable. Using proper management techniques can help you avoid odor problems.
To compost grass clippings you will need to:
Add bulky, high-carbon materials (browns)
Fresh grass clippings must be balanced with browns for the compost process to proceed without odor generation. Use browns that provide extra "bulk." Bulk keeps the compost from matting down and allows oxygen to enter the pile. Wood chips, leaves, cut up sticks, all provide bulk. You would probably want to avoid using paper as your primary brown if you are composting mostly grass clippings. While paper is a source of carbon, it has a tendency to mat down and could restrict airflow.
You can use either the "mix it" or "sandwich" methods of pile building. However, the mix it method tends to work better. If you use the sandwich method, make many thin layers, versus a few thick layers. For example, the green layer should be no more than 1-2 inches thick. This will help prevent the grass from matting down and creating anaerobic pockets. Always begin and end your pile with browns to help provide for air to enter the pile at the bottom and absorb odors before they are released from the top of your compost.
You may want to start with twice the volume of browns as grass. However, an actively managed bin can be constructed with less brown material.
NOTE: Bags or piles of grass clippings will go anaerobic very quickly, and whenever you open them up, you will release an "odor bomb" and then have a huge clump of grass to contend with. Therefore, do not store grass for later use. Instead, store browns.
Oxygenate (aerate) the pile
A well oxygenated compost system does not create odors like an anaerobic (no oxygen) situation. Using a bulky brown material will help, but if you are composting grass clippings, you must be committed to turning the pile periodically. This mixes the materials, thoroughly oxygenates the pile, and prevents anaerobic pockets from forming. You may need to turn the compost system more frequently in the first few weeks than when composting other materials.
If you plan on composting grass clippings on a regular basis, you might consider making or purchasing a rotating drum composting unit. This kind of system is known for its ease of turning and oxygenating the compost. As a result, the composting process is accelerated and you may be able to stabilize the grass clippings in a week. After the material is stabilized, it is less likely to create odor problems. It must be cured for a period to complete the composting process, but will greatly reduce the composting time period and may allow you to keep up with the weekly mowing schedule common during the summer months.
Manage two or more compost piles simultaneously
After beginning composting grass clippings one week, the composting process will continue for several more weeks. What do you do during the summer months when clippings are created each week? You'll have to create a second, or even a third bin.
So you might have a schedule like this:
- Week 1 – start compost bin 1
- Week 2 – turn compost bin 1 and start compost bin 2
- Week 3 – turn and consolidate compost bins 1 and 2 into bin 1, and then start composting again in bin 2
After a couple of consolidations, you will be able to set the compost to the side and let it finish the composting process without much more activity.
