Food Scap Composting

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Food Scrap Composting Flier

Properly composted food scraps can turn into an excellent fertilizer. However, composting food scraps in a regular backyard compost bin can be tricky. If done incorrectly, backyard composting of food scraps can attract some potential pests (ex. rats, mice, raccoons and opossums). Fortunately, there are three simple ways to compost your food scraps without fear of attracting potential pests.

Please keep in mind that all three of these methods are ONLY for composting fruit and vegetable trimmings, bread, rice, pasta, tea bags, coffee grounds, coffee filters and other such materials. Do NOT attempt to compost meat, fish, dairy products, pet waste or greasy food through these methods. These items can attract pests and cause problems during composting.

Option #1: Worm Composting

worm-bin-picVermicomposting, a.k.a., worm composting, is the practice of using worms to do your composting. The worms feed on your fruit and vegetable trimmings and decompose them for you. The goal of vermicomposting is to create the ideal environment for worms to thrive so they can efficiently decompose the material you feed them. Worm composting is simple. You need a box, bedding, fruit and vegetable trimmings, and worms.  More detailed information about worm composting.

Option #2: In-Ground Composting

in-ground-composting2This is perhaps the simplest and most pest-free method of composting food scraps.  Just bury your food scraps at least 8 inches deep in your garden. Garden soil provides a natural barrier that keeps out flies and other pests, and holds in moisture and odors. If you have dogs that like to dig in your garden, this approach may not be the best for you.

Food scraps can be buried in empty areas of vegetable and flower gardens, or in holes outside the drip line (below the ends of branches) of trees and shrubs. Use a shovel or post hole digger to dig a hole or trench about 1 foot deep. Add 2 to 3 inches of food scraps to the hole. Chop and mix scraps into soil, then cover the food scraps with at least 8 inches of soil to keep pests out.

Check occasionally for signs of digging by rodents, dogs or other pests. If you see signs of digging, it may be better to switch to a digester or worm bin.

Food scraps may take from 1 to 6 months to decompose depending on the season, moisture, soil and the type of food scraps that are buried. Seeds and small seedlings may be planted on top of buried food scraps immediately. Large transplants should not be planted until the food has decomposed. Do not bury more food scraps in the same place until the first scraps have been fully composted.

Option #3: Composting with a Food Digester

Please note: If you have pest problems with cockroaches, using a homemade food digester may not be a good composting method.  The food digester can serve as a breeding ground for cockroaches unless managed very carefully.  If you have cockroach problems, be sure to harvest your food digester as soon as you notice cockroaches inside or around the digester and wash the digester out thoroughly after harvesting.

food-digesterMaking a Food Digester

Another option for composting food scraps is using a homemade food digester. You can make your own using a galvanized metal garbage can (a 32 gallon can works well). The can should have a tight-fitting lid. Drill or punch about 20 drain holes, 1/4 or 3/8 inch diameter, in the bottom of the can. Drill 20 more holes in the sides of the can, but only in the lower third, which will be covered by soil.  TIP: if you drill from the inside of the bin to the outside, you won't have to worry about sharp, jagged metal around the drainage holes inside your food digester--the sharp edges will be pointed outwards into the soil.

It is very important to make sure that the lid fits snugly on the can to keep raccoons and other pests out. If the lid does not fit tightly you can make a lid out of a piece of ply-wood, with a handle on the top and some wood blocks underneath to fit the lip of the can and help hold the lid on. If needed, a bungee cord or rope can be attached to the lid handle and the can handles to secure the lid.

Dig a hole at least 15 inches deep in a well-drained area of your yard and set the can into the hole. The can should be 1/3 to 1/2 buried in the soil—none of the holes you drilled should be visible above the soil. Once the hole is deep enough, push the soil back in around the sides. Your new food digester is ready to use! You do not need to add worms to your digester—worms will find their way into the digester through the holes and will help break down the food scraps.

Composting With Your Digester

Now that your food digester is ready, you can start adding food scraps. You can collect your food scraps in a container in the kitchen, and place the food scraps in your food digester whenever is conveinent for you--every day, once or twice a week. Be sure the digester lid is on tight after adding the food scraps.

Harvesting the Compost From Your Digester

Depending on your household’s food habits and how large your digester is, the digester may fill in 4-12 months. Once the digester is full, the compost can be harvested.

Harvesting the compost is simple. While harvesting compost from your digester, watch out for the jagged metal around drainage and air holes.

Harvesting Option 1: Cure the compost. Shovel out the contents of the digester.  Place any un-composted material back in the digester for further composting (or try in-ground composting) and mix the compost with some soil, lay it in the sun and wait a week for it to turn drier and sweet smelling.

Harvesting Option 2: In-Ground Composting. This method essentially uses the food digester as a fermentation vat by breaking down your food scraps into smaller, manageable amounts. When the digester gets full, or whenever you feel like emptying it, simply shovel out the contents of the digester (fully composted, partially composted and fresh food scraps) and the compost in a trench in the garden, following the instructions for in-ground composting listed above.

Food Digester Trouble-Shooting

The best way to keep odors and fruit flies at a minimum is to make sure the digester lid always fits tightly. If flies and odor are still troublesome, stir in leaves or coarse sawdust to keep the food scraps aerobic. When adding more food scraps, you can also cover fresh food scraps with leaves, coarse sawdust, straw or shredded newspaper to exclude fruit flies. If you prefer to use grass clippings as a covering material, first leave them in the sun to dry out and turn brown. Keep in mind that adding dry material each time food scraps are added will make your digester fill up faster. Another way to cut down on flies in your food digester is to hang strips of fly paper on the inside of the digester lid. Once a healthy worm population is established in the digester, they will help reduce odors by aerating the food scraps. The inside of the digester may have a slightly unpleasant smell and some fruit flies—the goal is to make sure that the outside of the digester does not smell or have flies buzzing around.

It’s important to keep the lid on your digester closed to keep pests out. Place a rock on the lid or tie the lid handle to the handles on the sides of the garbage can to hold the lid on. Also, be sure to keep meat, fish, dairy and greasy food scraps out of your digester. They will smell bad and attract animals, so it is better to put them in the garbage.


Building Your Own Composting Bin: Designs for Your Community, California Department of Resources Recycling and Recovery (CalRecycle) Last Revised: June 2006.
Composting Yard and Food Waste at Home. The Natural Lawn & Garden, Healthy Landscapes for a Healthy Environment, sponsored by Seattle Public Utilities, 2005.
Homemade Food Scrap Digester, The Natural Soil Building Program, sponsored by Seattle Public Utilities and managed by the Seattle Tilth Association. Revised 12/03. 

More Information

Additional information about composting can be found on the California Department of Resources Recycling and Recovery website.