What Vermicomposting Is
Vermicomposting uses red wiggler worms (Eisenia fetida) to break down organic material through digestion rather than microbial decomposition alone. The output — vermicast or worm castings — is one of the most nutrient-dense soil amendments available. It contains five times more nitrogen, seven times more phosphorus, and eleven times more potassium than typical topsoil, according to research published by Cornell University's Cooperative Extension.
The process happens indoors at room temperature, making it particularly suitable for Canadian apartments and condominiums where outdoor composting is not possible. A well-maintained bin produces no noticeable odour and can process 0.5–1 kg of food scraps per week.
The Right Worms
Red wigglers (Eisenia fetida) are the species used for vermicomposting. They are not the same as the large earthworms you find in garden soil. Red wigglers are surface dwellers — they thrive in the top few centimetres of organic material, which is exactly where the composting action happens in a bin.
Do not use nightcrawlers or garden worms. They are subsoil species and will not survive in a bin environment.
Red wigglers are available from specialty composting suppliers, some garden centres, and online vendors. In Canada, suppliers in Ontario and British Columbia ship year-round in insulated packaging. A starting population of 500 g (roughly 500–1000 worms) handles the scraps of a two-person household.
Setting Up the Bin
Container options
A purpose-built vermicomposting bin (with drainage tray and ventilation) is the most convenient. The Worm Factory 360 and similar stacked-tray systems allow you to harvest vermicast from the bottom tray while worms migrate upward into fresh material. These cost $80–$150 CAD at garden centres.
A DIY bin using a plastic storage container (30–40 litre) drilled with ventilation holes works just as well for most households and costs under $20. Use two nested containers — the inner one holds the bin contents, the outer one catches leachate (worm tea).
Bedding
Bedding provides the worms' living environment. Use shredded newspaper, cardboard torn into small pieces, or coconut coir. Avoid glossy paper. The bedding should be moist — squeeze a handful and it should release just a few drops of water.
Fill the bin two-thirds full with moistened bedding. Make a well in the centre and place the worms on top; they will burrow in within a few minutes. Leave the bin undisturbed for the first 3–4 days while the worms acclimate.
Feeding the Worms
Add food scraps in small amounts buried beneath the bedding surface. Red wigglers prefer pre-composted or slightly aged material — scraps that have sat for a day or two are easier for them to process. Start with easy materials: fruit scraps, vegetable peelings, coffee grounds, and tea bags.
Worm-friendly foods
- Fruit and vegetable scraps
- Coffee grounds (excellent nitrogen source)
- Tea leaves and bags (remove staples)
- Crushed eggshells (adds grit and calcium)
- Bread and grains in small amounts
- Shredded paper and cardboard
Avoid these
- Citrus peels in large amounts (acidic, disliked by worms)
- Onion and garlic (mild deterrent)
- Meat, fish, and dairy (odour and pest attraction)
- Salty or oily foods
- Spicy foods
Feed the bin when the previous batch is mostly processed — approximately every 3–5 days for an active bin. Overfeeding is the most common beginner mistake and leads to odour and fruit fly problems.
Maintaining Bin Conditions
Temperature: Red wigglers thrive between 15°C and 25°C. Keep the bin away from heat sources and direct sunlight. In winter, position it in a warm indoor space — a kitchen cupboard, utility room, or heated basement. Below 10°C, activity slows significantly; below 4°C, worms can die.
Moisture: The bin should feel like a moist sponge throughout. If it gets too wet, add dry shredded newspaper. If it gets too dry, mist with water.
pH: Worms prefer a neutral to slightly acidic environment. Crushed eggshells help buffer excess acidity, which can build up when citrus or coffee grounds are added frequently.
Aeration: The bin needs oxygen for aerobic decomposition. Turn the bedding lightly with a fork every week or two to prevent anaerobic zones.
Harvesting Vermicast
After 2–4 months, you will notice the bin material turning dark, crumbly, and earthy-smelling. That is vermicast ready for use.
The simplest harvest method: push all the bin contents to one side, fill the empty side with fresh moistened bedding and food scraps. Over 2–3 weeks, the worms migrate to the fresh side. Remove the finished vermicast from the original side — most worms will have left it. Check for worm cocoons (small lemon-shaped capsules) and return them to the active side.
For stacked-tray systems, harvest from the bottom tray once it is full of finished castings and worms have migrated upward.
Using Worm Leachate
The liquid that drains from the bin is called leachate or "worm tea." It contains soluble nutrients and can be diluted 10:1 with water and applied to houseplants or garden soil. Do not apply it undiluted — it is concentrated enough to burn plant roots. Use it within 24–48 hours of collection for best results.
Troubleshooting
Fruit flies: Always bury food scraps and keep a layer of bedding on top. A cover of damp newspaper directly on the bedding surface eliminates most fly problems.
Unpleasant odour: Usually caused by overfeeding or too little bedding. Remove excess food, add shredded cardboard, and aerate the bin.
Worms escaping: Worms explore after being disturbed or if conditions are unfavourable. Turn on a overhead light near the bin for a few hours — worms retreat from light. Check moisture levels and temperature.
Slow processing: If the bin is not processing food at the expected rate, population may be too small, temperature too low, or the food type requires longer breakdown. Chop scraps into smaller pieces to speed up processing.