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Food Scrap 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 (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.

You CAN place meat, fish, dairy, fruits and vegetables, breads, etc. in your organics cart for composting--those materials are sent to a professional compost facility that operates at high temperatures and is able to avoid pests and other pathogens.

Option #1: Worm Composting

worm-bin-picVermicomposting, a.k.a., worm composting, is the practice of using worms to compost your fruit and vegetable trimmings. The goal of worm composting 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

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 sized 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 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. 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.

You can collect your food scraps in a container in the kitchen and place the food scraps in your food digester whenever is convenient 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. After the digester has been established for at least 3 months, the first materials that you added should be at least partially composted. You can harvest compost from the digester when it is full or at any time you wish after the first 3 months. While harvesting compost from your digester, watch out for the jagged metal around drainage holes.

Harvesting Option 1: Shovel out the contents of the digester.  Place un-composted material back in the digester for further composting.  Mix the compost with some soil, lay it in the sun and wait for it to dry.

Harvesting Option 2: 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, shovel out the contents of the digester (fully composted, partially composted and fresh food scraps) and follow the instructions for in-ground composting.

Food Digester Trouble-Shooting

If you have 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.

The best way to keep odors and fruit flies at a minimum in your homemade digester is to make sure the digester lid is always tightly closed. If necessary, tie the lid handle to the handles on the sides of the digester 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 organics cart.

 If flies and odors are still troublesome, stir in leaves or sawdust to keep the food scraps aerobic. When adding more food scraps, you can also cover fresh food scraps with leaves, 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 manage flies in your food digester is to hang strips of fly paper on the inside of the digester lid.

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. Once a healthy worm population is established in the digester, they will help reduce odors by aerating the food scraps.

Sources:

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.