Frequent Questions

What can be done to prevent odors and pests when composting?

Separating food waste from the MSW stream at the source actually alleviates problems with odor and pest at landfills. The compost process produces little odor as long as the system is properly aerated and materials are properly mixed.


If incoming ingredients have been stored in low-oxygen conditions for a week or more and have become anaerobic, they will impact the smell of the compost stream to which they are added. To avoid odors, composting requires a proper balance of “green” organic materials (e.g., grass clippings, food scraps), which contain large amounts of nitrogen, and “brown” organic materials (e.g., dry leaves, wood chips, branches), which contain large amounts of carbon but little nitrogen. Adding a dry bulking amendment such as wood chips increases porosity, which means an increase in the oxygen able to penetrate the compost. Keeping moisture levels down and aerating regularly will also help reduce odors. Learn how to identify different smells associated with composting Exit EPA and how to avoid those odors.

To minimize odors at the collection source, empty collection containers regularly and periodically rinse them with soap and hot water. Washing collection bins will resolve odor challenges.

If a worm bin smells bad, it probably has too much food waste, it's too wet, or there is cheese or other animal products (e.g., meat) present. To eliminate bad odors, remove excess or inappropriate wastes and add fresh bedding. Removing the lid for a while will also allow some of the moisture to evaporate.


To avoid pests, do not backyard-compost meat, bones, and fatty foods such as cheese, salad dressing, and cooking oil. The odors created by these foods can attract rodents and other animals. Food scraps should be buried in the middle of the compost pile to keep pests and rodents away. Covered bins also reduce attracting pests to compost piles. In-vessel systems, including most vermicomposting systems, provide the highest protection against rodents and other animals. These systems are usually fully enclosed and are often lockable.

One of the most common pest problems with worm composting food scraps are vinegar or "fruit" flies. Although fruit flies are not dangerous and they don’t bite, they can be annoying. To help minimize the incidence of fruit flies in your food scraps or worm bin:

  • Wrap fresh food wastes in newspaper.
  • Cover fresh food wastes with a few inches of worm bedding or castings
  • Freeze the food scraps overnight before adding them to the bin.

When collecting large amounts of food waste, you can minimize pest problems by using appropriate, leak-proof collection containers, regularly emptying of these containers into larger onsite collection bins, and frequent collection by the hauler. California's Integrated Waste Management Board's Compost and Mulch Exit EPA page has more information on composting for large operations.

Visit the "Troubleshooting Composting Problems" table on Exit EPA for more tips on how to reduce common problems, including odors and pests. The California Integrated Waste Management Board also provides troubleshooting tips Exit EPA to learn how to avoid pests and odors.


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