How Do I Set Up a Worm Composting System?

Worm composting — or vermicomposting — uses a specific type of compost worm to break down organic material, particularly kitchen waste, into an exceptionally rich compost much faster than a conventional heap. The finished vermicompost is highly concentrated in nutrients and beneficial soil biology. A wormery takes up very little space, works well indoors or in a shed, produces no unpleasant odour when managed correctly, and is one of the most efficient ways to deal with kitchen vegetable scraps in a small garden or flat.

Setting up a wormery

A wormery needs a container with drainage, bedding material, and a starter population of worms. Purpose-built wormeries with multiple stacking trays are the most convenient option, but a large plastic bin with drainage holes drilled in the base works well. Fill the bin with damp bedding — shredded cardboard, torn newspaper, or coir — to a depth of 10–15 cm. Add the worms (typically purchased as 250g–500g of worm mix) to the bedding and allow them to settle for a day before adding food. Keep the wormery in a location that stays between 10–25°C — worms become sluggish in cold and stressed in heat.

Feeding the worms

Worms eat fruit and vegetable peelings, tea bags, coffee grounds, and crushed eggshells very efficiently. Avoid meat, fish, dairy, oily foods, onions and garlic in large quantities, and citrus peel — these either attract pests, produce harmful acidity, or are too strongly flavoured for the worms to process comfortably. Add food in relatively small amounts every few days rather than large quantities at once. Cover new food with a layer of cardboard or the wormery blanket to deter fruit flies.

Harvesting vermicompost

After two to three months, the lower portion of a single-bin wormery, or the bottom tray of a stacking system, will contain finished vermicompost — dark, crumbly material that smells earthy. Harvest it by pushing the contents to one side and adding fresh bedding to the other — the worms migrate toward the new material over several days, allowing you to remove the finished compost from the vacated side. Use vermicompost as a top dressing for houseplants, in potting mixes (diluted to 20–30% with other compost), or as a rich amendment for seed-starting.