Worm composting, or vermicomposting as it's known in scientific circles, is a clean and convenient method for disposing of kitchen food waste. Outdoor composters can generate unpleasant odors and attract insects unless carefully managed. With a worm bin, worms do most of the work. As long as you don't give the worms more food than they can process, your bin should stay free of odors and flies. However, some foods can be problematic. Vegetables such as broccoli smell badly as they decompose, and banana skins can breed fruit flies (see Reference 1, page 69).
Worm Bin Basics
A standard worm bin is usually made from a wooden box or plastic tote. Worms feed near the surface, so they're usually only 12 to 16 inches deep. The bins are kept covered because worms like the dark, but the lid and sides are usually perforated to allow air circulation. The bin is filled with damp bedding, consisting of shredded paper, straw, peat moss or similar materials, to provide the worms with both habitat and food. The worms are red worms, smaller cousins of the familiar earthworm. They're sold in garden centers and bait shops (see Reference 1, pages 64 to 66, and Reference 2, pages 12 to 15).
A pound of red worms is capable of consuming anywhere from 1/2 to 1 pound of food each day. Since the bedding provides some of that, it's usually best to be conservative and aim for 1/2 pound per day. If you give the worms more food than they can eat in a day, the scraps are more likely to attract flies. You can also minimize flies by covering the bin's vent holes with window screening and pushing the food scraps down into the bedding. However, banana skins require extra measures (see Reference 1, pages 64 to 66, and Reference 2, pages 12 to 15).
Fruit Flies and Banana Skins
Bananas and citrus fruit are often the source of fruit flies in a home. They're especially prone to bearing fruit fly eggs on their skins. The risk of a major infestation can be minimized somewhat by washing the fruit with hot soapy water when you first bring it home. Chop the banana skins before you put them in the bin. Worms can process small pieces more quickly, giving the skins less time to attract fruit flies. Freezing the skins or microwaving them for 60 seconds kills fruit fly eggs and reduces the likelihood of an infestation (see Reference 1, page 69).
Fruit Fly Traps
If banana skins or other food wastes have prompted an infestation of fruit flies around your worm bin, don't despair. Construct a fruit fly trap by placing a piece of banana skin inside a jar and covering it with plastic wrap. Poke holes in the wrap with a toothpick so that flies can enter. Place the trap on a shelf above the bin and a few feet away (see Reference 3). Empty it outdoors each day until the fruit flies are gone. Cover the bedding with a sheet of plastic wrap to prevent reinfestation by limiting fruit flies' access to the bin.
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