Homemade worm compost bin: build a 3-tier stacking bin

• Top and middle bins: house the worms. Holes in the bottom let worms crawl upward to follow the food.
• Bottom bin: collects liquid (leachate). Fit a tap so you can drain it. This liquid is not the same as brewed worm tea — dilute it well if you use it on plants.
• Lid: keeps light, rain and predators out.

1. 1Drill drainage holes in the two worm bins

   Start with the two bins that will house the worms. Drill plenty of holes about 5–8 mm into the bottom of both, spaced about 5 cm / 2 inches apart. These holes stop flooding (worms drown without oxygen) and let worms crawl up into the next tray to follow the food.

   

2. 2Drill the tap hole in the bottom bin

   Drill a hole for the tap in the front of the third bin (the leachate collector). Use a hole saw just a fraction bigger than the tap. Place the hole as low as you can while leaving room to tighten the nut inside. No tap? A wine cork works as a temporary plug.

   

3. 3Attach the tap

   Push the tap through, add the washer and tighten the nut on the inside so it does not leak.

   

4. 4Make a lid if you need one

   If your bins came with a lid, use it. Otherwise cut a plastic sheet 3–5 mm thick to the size of the bin: place a bin upside down on the sheet, mark the edges, and cut with a jigsaw or strong scissors.

   

   

   

   

5. 5Assemble and place in the shade

   Stack working bin(s) on the collecting bin, put the lid on, and you are ready. Outdoors, put a flower pot or brick on the lid against wind. Never leave the bin in full sun — heat can kill the worms. Good spots: under a tree, in a garage or shed. Compost worms cope with about 5–29 °C (41–84.2 °F), and they do best at 15–25 °C (59–77 °F).

   

Add moist bedding (shredded cardboard or newspaper), then your compost worms, then a little food under the bedding. Coffee grounds: feed sparingly. Follow starting a worm farm for the first weeks. Do not overfeed while the herd is still small.

When the lower working tray is mostly finished castings, add fresh food in the tray above. The worms migrate up. Then empty the lower tray. Full walkthrough: harvesting worm castings from stacking bins.

Outdoors needs shade and predator protection. Indoors needs a close-fitting lid and careful moisture control so you do not get flies or smells. See indoor worm farm. Compare other designs on types of worm bins.

Start with about 500 to 1,000 compost worms in a typical household 3-tier bin and enough moist bedding to fill the working tray several centimetres deep. Shredded cardboard and newspaper are excellent. Coffee grounds: feed sparingly. Add food under the bedding, not in a heap on top, to discourage flies.

Open the tap regularly so the working trays never sit in a flood. The liquid is leachate, not brewed worm tea. Dilute it well (for example 10:1 with water) if you use it on ornamentals, or discard it if it smells foul. For true tea, brew castings with molasses and air — see worm tea.