A worm bin is a wood or plastic container with a lid. The dimensions can vary depending on the size of the operation. A guideline is 1 square foot of bin for every pound of food waste put in the box at any given time. Boxes should be shallow. Piled up food waste will begin to compost thermally, producing heat. Because the worms are trapped in the box, the heat can kill them.
The sides of the box should have holes covered with screen to allow for ventilation while preventing flies from becoming a problem. The lid should keep light out, as worms prefer a dark environment. As the worms reproduce and the vermicompost system expands, bins can be added and stacked on top of each other.
Worm binds made of stacking, shallow trays are also commercially available and can be constructed with a little ingenuity.
- Plastic or wood storage bin with removable, snug-fitting lid that measures roughly 18 inches wide, 24 inches long, and 8 inches deep. Dimensions can vary.
- Utility knife or 2 inch hole saw
- Silicone or other adhesive
- Window screen
- Using either a utility knife or hole saw, cut two, 2 inch holes on each of the long sides of the bin, near its top.
- Cut pieces of window screen slightly larger than the holes.
- Attach to the outside of the bin, over the holes, using silicone or other adhesive. Make sure that the bad of adhesive expands the entire circumference of the hold so worms will not be able to escape.
- Allow silicone to cure.
- Add bedding, worms, and food.
Fill 3/4 of the box with bedding. The bedding absorbs excess moistures and is something to bury the food under. The best bedding is shredded newspaper. It can also be made from cardboard, sawdust, old leaves, or straw. Bedding is a starting material: the worms will eventually eat the bidding and turn it into castings. More bedding can be added if moisture becomes a problem, but the works are generally happy to live in their own castings.
A worm has no teeth. It can only eat what it is able to pass its body through, making soft foods ideal. Smaller pieces of food are more quickly digested. Avocados, mangos, bananas, apples, melon, coffee grounds, pasta, rice, tofu, and tomatoes area all favorite worm foods. Worms do not handle meat, dairy, oils, or spicy foods well. Initially, give the worms small amounts of food. Add more only when it has all been eaten.
Moisture and Temperature
Moisture levels need to be monitored. A slight dampness is ideal. Too much liquid will make the box go anaerobic and kill all the worms. Too little moisture will dry them out.
As worms do best in temperatures in the human comfort range, indoor vermicomposting is easier. Outdoor operations must be insulated and heated.
Harvesting and Using the Castings
Periodically, the casting should be harvested for use as a fertilizer. The easiest way is to push all the material in the bin to one side and place fresh food and bedding on the other side. The worms will migrate to the new food, leaving the old castings worm-free and ready to harvest. Another method is to spread the finished compost on a screen with holes big enough for the worms to crawl through. Put the screen in the sun. The light-sensitive worms will burrow away from the top layer. Keep removing the wormless layer until all the worms have crawled though the screen.
Worm castings can be applied directly as a fertilizer to gardens. They can also be used to make compost tea.