Vermicompost is compost made by worms — specifically the dark, crumbly castings that red wiggler worms leave behind after eating kitchen scraps and bedding. It is one of the richest soil amendments a home gardener can make: worm castings hold nutrients in a slow-release form, carry a large and diverse community of soil organisms, improve soil structure, and hold moisture well. A small worm bin under the sink or in a shed can turn a household's vegetable peelings into a steady supply of premium fertiliser, with no smell when it is run properly. This guide explains how to set up a worm bin, what to feed and what to avoid, how to harvest castings, and how to use them.
Vermicomposting suits gardeners who have more kitchen scraps than garden space, who want compost in winter when an outdoor heap slows down, or who grow in containers and need a concentrated, gentle feed. It does not replace a garden compost heap for bulk material — a worm bin processes scraps, not the autumn leaf fall — but as a complement it is hard to beat.
How vermicomposting works
Red wigglers (Eisenia fetida) are surface-dwelling worms that live in the top layer of soil and leaf litter, eating decaying organic matter. In a worm bin they eat through bedding and food scraps, and their gut bacteria and the microbes in the castings break the material down further. The result — worm castings — is finer and more nutrient-rich than ordinary compost, with nutrients held in forms plants can take up slowly over weeks. Castings also contain plant growth compounds produced by the worms' gut bacteria, and they improve soil structure by adding stable aggregates that hold air and water.
A healthy bin has no bad smell: it smells like damp earth. Smell means something is wrong — usually too much food, too much water, or not enough air. Worms breathe through their skin, so the bedding must stay damp like a wrung-out sponge, never wet and never dry. They also need darkness and a temperature between roughly 15°C and 25°C. Below 10°C they slow down sharply; below freezing they die; above 30°C they suffer. That is why indoor bins, garages and shaded sheds work better than bins left in full sun.
Setting up a worm bin
You can buy a stacking worm bin or make one from two plastic storage boxes. A bin for a household needs roughly 30–40 litres of capacity to start, with a lid and drainage holes in the base so excess liquid can escape. Drill small air holes around the sides near the top, and put a tray underneath to catch liquid — the liquid, known as worm leachate, can be diluted 1:10 with water and used as a mild liquid feed, though it is not the same as compost tea and should never be used undiluted.
Bedding is the worms' home and their first food. Shredded newspaper, cardboard, coconut coir or leaf mould all work; shredded cardboard and newspaper are the cheapest and most available. Soak the bedding, wring it out until it is damp like a wrung-out sponge, fluff it up loosely in the bin to about 15 cm deep, and add a handful of garden soil or finished compost to introduce microbes, plus a small handful of crushed eggshells for grit and calcium. Then add the worms — about 500 g (roughly 500–1,000 worms) is a good starting population for a household bin — and leave them alone for a few days to settle in before feeding. See our coco coir for plants guide if you use coir bedding, and our eggshells in garden guide for the eggshell habit.
What to feed worms — and what to avoid
Feed little and often, and bury the food under the bedding so it does not attract fruit flies. Good foods include vegetable and fruit peelings, tea bags (plastic-free only), coffee grounds, crushed eggshells, stale bread in small amounts, and shredded paper. Chop or tear food small so it breaks down faster, and add a new portion only when the previous one is mostly gone — usually every few days. A useful rule is to feed roughly the worms' own weight in food per week at first, increasing as the population grows.
Do not feed meat, fish, dairy, fats, oils, cooked food in large amounts, onions and garlic in quantity, citrus peel in large amounts, or pet waste — these cause smells, attract pests, or harm the worms. Spicy food and salty food should also be avoided. If the bin starts to smell, stop feeding for a week, add dry shredded cardboard, fluff the bedding to let air in, and check the drainage. Fruit flies are the most common nuisance: bury food well, cover the surface with a sheet of damp newspaper, and keep the lid on.
Harvesting worm castings
After three to six months, the bin will be full of dark, crumbly castings and the original bedding will be mostly gone. There are two easy harvest methods. The light method: push the contents to one side of the bin, add fresh damp bedding and food to the empty side, and wait a week or two — the worms migrate to the fresh food, and you can scoop out the finished castings from the old side. The light method: tip the contents onto a sheet in bright light, and the worms burrow away from the light to the bottom; brush the castings off the top in layers until you reach the worm cluster, then return the worms to fresh bedding. Harvested castings should smell earthy, not sour. Store them in a breathable bag or bucket, not sealed plastic, and use them within a few months.
How to use vermicompost
Worm castings are gentle — they rarely burn plants — but they are concentrated, so a little goes a long way:
| Use | How much |
|---|---|
| Top-dressing vegetables | A 1–2 cm layer around plants, or a handful per plant, every 4–6 weeks |
| Seed starting | Mix 1 part castings to 3–4 parts seed starting mix |
| Potting mix | Mix 1 part castings to 4 parts potting mix |
| Transplanting | A handful in each planting hole |
| Houseplants | A thin top-dressing or a handful mixed into the top few centimetres, every 2–3 months |
| Compost tea | Steep castings in water as described in our compost tea guide |
Castings work well on seedlings and transplants because they are mild and biologically active. For heavy feeders such as tomatoes and cucumbers, castings are a good supplement to a full feeding routine, not a replacement for it — see our fertilizing vegetables guide. For houseplants such as monstera deliciosa, a small top-dressing twice a year is usually enough.
Common mistakes
The most common mistake is overfeeding, which causes smells, flies and unhappy worms. Feed less than you think, and wait until food is gone before adding more. The second is letting the bin dry out or flood — check moisture weekly and keep it like a wrung-out sponge. The third is using the wrong worms: ordinary garden earthworms are deep burrowers and do poorly in bins, while red wigglers are the right species. The fourth is putting the bin in full sun or a freezing garage. The fifth is feeding meat, dairy or oily food. And the sixth is expecting instant results — a bin needs a few months to build a population and produce its first harvest, but after that it produces steadily all year.
Safety notes
Wear gloves when handling worm castings and leachate, and wash your hands before eating. Do not use leachate undiluted, and do not use it on leafy crops close to harvest. Use only vegetable-based kitchen waste in the bin — never pet waste or meat. If the bin smells strongly or the worms are trying to escape, something is wrong with moisture, food or air; fix the conditions rather than adding chemicals. If you are unsure about safe composting practice, check your local extension service for advice.
Frequently asked questions
How long does it take to make vermicompost?
Expect the first harvest after three to six months from setting up a new bin, as the worm population builds. After that, you can harvest a portion every two to three months. A well-run bin produces steadily all year if it is kept indoors or in a frost-free place.
Can I use ordinary garden worms in a worm bin?
No, not well. Garden earthworms are deep burrowers that need soil depth and do poorly in the shallow, food-rich environment of a bin. Red wigglers (Eisenia fetida) are surface feeders that thrive in bins and are the species to buy or obtain.
Why does my worm bin smell?
Smell usually means overfeeding, excess water, or poor airflow. Stop feeding for a week, add dry shredded cardboard, fluff the bedding, and check the drainage holes are clear. A healthy bin smells like damp earth, not like rotting food.
How much worm casting should I use?
A little goes a long way: a handful per plant as a top-dressing, or one part castings to three or four parts potting mix. Castings are gentle and rarely burn plants, but there is no benefit in using more than the recommended amounts — save the surplus for the next round.
Is worm leachate the same as compost tea?
No. Leachate is the liquid that drains from the bin, and it can contain compounds you do not want undiluted. Dilute it at least 1:10 with water before using it on soil, never use it on leaves close to harvest, and do not confuse it with aerated compost tea, which is brewed deliberately from mature compost.