Using worms to turn household garbage into fertilizer is a part of permaculture, a term that's short for "permanent agriculture." The aim of permaculture is to design and build ecologically friendly habitats in which humans live in harmony with plants, animals, soils and water in a productive, stable system. Worm farms turn biodegradable waste into worm castings, useful for potting soil and as a nutrient-rich compost--which is a basic permaculture concept.
Plastic Tub Farm
Drill a series of small holes on the bottom and sides of a plastic tub that has a lid. The side holes provide air for your worms; the bottom holes allow for drainage. Put bricks between the tub and a pan or plastic catch basin under it, so the tub doesn't sit directly in the drained fluid. Put a layer of small stones in the bottom of the plastic tub to help drain it. Layer an inch of damp newspaper on top of the pebbles, then add household garbage and other biodegradable waste.
For a larger system, use a bathtub (if this is at all viable in your situation). Tubs are designed to drain. Put the tub high enough so you can put a small bucket under the drain. Fill the tub two-thirds full of manure and one-third of scraps or compost. Top with a cover that will block the light but let rain in. Add 1,000 worms.
Uncovering and recovering the farm, feed the worms about five gallons of scraps each week. Each day collect worms in the fresh scraps that you put in the day before; put the worm castings into a pile. The worms, fleeing the light, will be gone in 10 to 20 minutes. Remove the outside 1 1/2 inches of castings to a separate pile; keep repeating as the worms burrow toward the center of the tub.
Two kinds of worms are most often used for worm farms. The first, Eisenia fetida-- also called a red worm, red wiggler, branding worm, and manure worm--are 1 1/2 to 2 inches long and will live 2-5 years. They produce from two to five cocoons each week; each cocoon will hatch two or three worms in about a month and a half. The second worm, Lumbricus rubellus--also called the angle worm, garden worm, drift worm, or red march worm--grows to about 4 inches long
A worm will eat its own weight in food every day. They'll eat anything, but avoid feeding them citrus, pineapple, onions or meat scraps. You can feed them coffee grounds or moistened paper or cardboard. An excess of fresh grass clippings can generate heat in the compost that will kill your worms. If mold is growing on your worm farm, you've been feeding them too much (mold grows on what they don't eat).
In cold climates, worms will go dormant in the winter. You shouldn't feed them, but you should insulate them. Straw bales make good insulation.
Keep your farm in a shady place. Your waste mix should not be too dry. Spray it at regular intervals. If it is too wet, it will smell like methane.
The liquid that drains from your worm farm is called leachate. Diluted 20 to one with water, it can be used as a "worm tea" to fertilize plants.
Worm castings are pH neutral; they smell and look like good soil but they have five times more nutrients. You can add castings to potting mixes or substitute it for compost.