The hobbyists who raise compost worms, an inventive group of do-it-yourselfers and tinkerers, will try anything from salvaged bathtubs to Rubbermaid totes to provide a hospitable and low-cost habitat for their red wigglers. Some expand their growing worm colony from a simple one-compartment bin to stackable bins with multiple levels. Others design an exciting variation on setups used by commercial vermicomposters: They create small-scale, flow-through worm bins.
Commercial vermicomposters in temperate areas of the world set up long, shaded outdoor bins with a metal grate bottom. They continually add food and complementary bedding materials such as paper and cardboard to the top of the bin. The worm’s castings (manure) drop to the bottom of the bin. The worms themselves continually migrate upward to within the highest 4 inches of the bin.
A scraper bar pulled by a winch periodically scrapes along the top of the grate, pushing the castings through it to the ground, where they can be swept up and placed on gardens.
Home hobbyists simplify this strategy by adapting a 55-gallon drum, rain barrel or wheeled outdoor trash can to work as a flow-through worm bin.
To create a flow-through worm bin, cut a window using a jigsaw on the side, near the bottom, of a 55-gallon drum. A window 12 inches across and 5 inches deep, with its lowest edge 2 inches up from the ground, should suffice.
Drill 3/8-inch holes 3 inches above the top of the window suitable to accept 3/8-inch threaded, zinc-plated bars to create a grid, with the centers of each rod about 1 ½ inches apart. Align the grid holes so that you can introduce a three-tined garden cultivator via the window to later scrape completed worm castings out of the bottom of the bin. Cut the bars to fit and thread them like skewers through the holes.
Place six layers of newspaper across the grid. Add 10 inches of worm bedding material, such as soaked cardboard strips, shredded paper, peat moss or coconut coir (fiber). Introduce food scraps in a pocket in the bedding about 4 inches deep, cover the pocket over and gently add red wiggler worms. Add three untorn damp sheets of newspaper across the top of the drum contents to discourage fruit flies. Cover the drum with a lid.
Feed the worms when the food in the original pocket disappears. Be prepared for the worms to process food more quickly than in shallow worm bins.
Remove castings by reaching in the window at the bottom and scraping upward between the grid rods with the cultivator tines.
Some hobbyists have experimented with adding a scraper bar of PVC, with the grid rods threaded through holes drilled in the PVC, but others note the simple design works fine without a scraper bar.
Add a dolly or board with casters underneath to permit moving your bin around, as it will likely become quite heavy.