DIY worm bins can be made of timber or from recycled containers such as plastic tubs or boxes, dustbins or water butts – here are just a couple of simple ideas to give you inspiration. (See my page on Worm Composting for more details of how to feed and take care of the worms.)
Single unit method
For this you will need a plastic dustbin (or a wooden or plastic box with a lid) to keep the worms in and the rain and flies out. Drill drainage holes around the base about 5cm up and about 25cm apart. Then drill some small holes 5cm down from the top of the bin as air holes. Stand the bin above a tray to collect the liquid plant food which leaches out as the compost matures. A plastic drainage tap (use a water butt or home brewing tap) can be fitted close to the base of the bin as an alternative to drilling holes – this will allow you to easily draw off the rich liquid plant food formed as the compost matures.
Put a 10cm layer of gravel or sand in the bottom, then cover with a layer of fibrous matting or a circle of wood or plastic with holes drilled through for drainage. Add a 7-10cm layer of moist bedding material, such as leaf mould, well rotted compost, or moist shredded paper, and the bin is now ready for the worms. Tiger worms or brandlings can be harvested from an existing worm bin, a manure heap, or a mature compost heap, or they can be purchased from fishing tackle shops, ebay, or worm bin suppliers such as The Recycle Works.
After adding the worms, place a few handfuls of food in the bin and cover it with a moist newspaper or cardboard. Put on the lid and leave undisturbed for a week to allow the worms to settle in. Gradually build up the food supply as the population of worms increases.
This system uses three 8-10 gallon plastic stacking storage boxes – the sort often sold for storing toys. They should be opaque, not see-through, and should stack quite tightly inside each other. You will only need one lid. More layers can be added later if needed.
Drill about twenty evenly spaced 1/4 inch holes in the bottom of two of the boxes. These will provide drainage and allow the worms to crawl up through the compost from box to box so you can harvest the castings.
Using a 1/16 inch bit, drill ventilation holes about an inch apart near the top edge on each side of the two boxes, and drill about 30 small holes in the top of the lid.
The bottom box doesn’t need any holes as it will be used for drainage and to catch any materials or worms falling down through the holes. To begin with you will just need to use this box, one of the boxes with the holes, and the lid.
Sit one of the boxes with holes inside the bottom box. Place a 3-4 inch layer of bedding material in the top box. This needs to be moist but not soggy. Use moist newspaper or shredded paper fluffed up and if possible add some leaf litter or well rotted compost, plus a little garden soil to provide grit for the worms.
Then add your worms to the bedding, and put some moist cardboard over the bedding – the worms will gradually eat the cardboard, and it will help to prevent fruit flies. Put on the lid and place the worm bin out of direct sun in a well-ventilated area such as a utility room, shed, garage, or balcony, or under the kitchen sink. This system is not rain-proof so is not suitable to sit outside.
Feed the worms just a little at first, placing the food under the cardboard. As they multiply, you can slowly increase the food supply. Harvest any liquid that drains into the bottom box – this ‘worm tea’ is a good liquid fertilizer when diluted with water.
When the first box is full, the next box is added on top. Place new bedding material in the second box and sit it directly onto the surface of the compost in the first box. Bury some food scraps in the bedding of the second box, cover with moist cardboard and put on the lid. The worms will migrate up through the holes to the fresh material and gradually, over one to two months, will leave behind almost worm-free vermicompost in the bottom box ready to be harvested. (You can rescue any worms that might remain, or just put them into your garden with the compost).