A worm bin or worm composter is the container that holds the worms in a vermicomposting, or worm composting, system. Worm composters are usually kept indoors, at least during cold months when the worms might freeze. Vegetable scraps, eggshells, and coffee grounds are fed to the worms, who produce worm castings that are a valuable garden compost. It’s a great choice for people who want to live their everyday life in a more eco-friendly fashion, since landfill use is reduced and high-quality organic compost is produced. When managed properly, a worm composter is free of odors and does not attract insects.
A variety of materials can be used to make a worm composter. Plastic or rubber bins are popular. Galvanized metal tubs and wood boxes can also be used. Do-it-yourselfers often reuse discarded materials in ingenious ways, as in a worm composter made of old tires. Commercially made worm composters are often made from post-consumer recycled plastic or other recycled materials. The material should be opaque, not transparent or translucent.
The size of the worm composter should be suitable for the number of worms it will contain and the amount of garbage they will be fed. Usually a ten-gallon (37.85 liter) worm composter will house a pound (0.45 kg) of redworms and process about one-half pound (0.25 kg) of food waste every day. This is a good size for two people. The worm composter should not be more than 23 inches (58.4 cm) deep and can be much less, since worms live near the surface of the soil. There should be a tray under the main body of the worm composter to catch any liquid runoff, which is a good compost tea for the garden. The worm composter should have a lid to keep the interior of the bin dark.
Good ventilation is important. A ten-gallon (37.85 liter) worm composter should have 20 to 30 holes drilled in the bottom and along the sides. The holes should be 1/16 to 1/4 inch (1.6 to 6.35 mm) in diameter.
A successful worm composter can be made of just one bin with a lid and a tray. Many people prefer a worm composter with several shallow stacked bins. This structure makes it easier to harvest the worm castings every month.