How Do You Start Vermicomposting (Worm Composting)?
To start vermicomposting, fill a ventilated plastic bin with damp shredded paper, add about 1 lb of red wiggler worms, and bury small amounts of fruit and vegetable scraps. Keep it at room temperature and damp like a wrung-out sponge, and you can harvest worm castings in roughly 3 to 6 months.
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What you need to start a worm bin
A worm bin is a shallow, dark, damp box with air holes, bedding, worms, and food. You can buy a stacking system or make one from a plastic storage tote for very little money. Both work. The worms care about moisture, air, and temperature, not the brand.
Bin size and shape
Shallow and wide beats deep. Red wigglers feed in the top few inches, so surface area matters more than volume. A 10 to 18 gallon (40 to 70 L) plastic tote, about 8 to 12 in (20 to 30 cm) deep, suits one or two people. A common rule of thumb is about 1 square foot of surface (0.1 m²) for each pound of food scraps you add per week.
Opaque bins are better than clear ones. Worms avoid light.
Drainage and airflow
Worms breathe through their skin, so they need air and they drown in standing water.
- Drill 8 to 12 holes of about 1/4 in (6 mm) in the bottom for drainage.
- Drill a row of similar holes around the upper sides and in the lid for air.
- Set the bin on bricks or blocks over a tray or a second lid to catch any liquid.
The liquid that drains out is called leachate. It is mostly water that ran through rotting food, not the same thing as finished castings. Pour it on an outdoor bed or dilute it heavily before using it on plants.
Bedding
Bedding is the brown, carbon-rich layer the worms live in. Good options:
- Shredded newspaper or plain cardboard torn into strips
- Coconut coir, soaked and squeezed out
- Dry leaves, shredded
- A handful of garden soil or finished compost to bring in helpful microbes
Wet the bedding until it feels like a wrung-out sponge, then fluff it into the bin until it is about two-thirds full. Add a handful of crushed eggshells for grit and to help buffer acidity.
Which worms to use
Use red wigglers (Eisenia fetida), sometimes sold as red worms, tiger worms, or manure worms. They live in surface litter and rotting organic matter, tolerate crowding, and breed quickly in a bin. Garden earthworms and nightcrawlers are the wrong worms. They burrow deep in soil and will not thrive in a box of scraps.
Buy them from a worm farm or a local vermicomposter, not a bait shop, unless the bait shop sells red wigglers by name.
How many worms to start with
A common starting rule is about 1 lb (450 g) of worms for roughly 0.5 lb (225 g) of food scraps a day. That is an approximate figure. New worms eat less while they settle in, and a fresh bin has few of the microbes that break food down first.
In practice, start with 1 lb of worms and feed a cup or two of scraps two or three times a week. Increase as you see food disappearing within a few days. The population will grow to match the food supply over a few months.
What to feed worms
Worms eat the microbes and soft rotting material on food, not the food itself. Small, soft pieces break down faster, so chop or freeze scraps before adding them. Freezing and thawing bursts cell walls and speeds things up.
| Category | Examples | Why | How to add |
|---|---|---|---|
| Feed freely | Fruit and vegetable scraps, coffee grounds, tea leaves, melon rinds, squash, leafy greens, crushed eggshells | Soft, moist, mild | Bury under bedding in a different spot each time |
| Feed sparingly | Citrus peels, onions and garlic, bread, rice and pasta, tomatoes | Acidic, strong-smelling, or prone to mold | Small amounts, mixed with extra bedding |
| Avoid | Meat, fish, dairy, oils and greasy food, salty or spicy food, pet waste | Smell, pests, harmful to worms | Keep out of the bin entirely |
Coffee grounds are a worm favorite but can heat up in large amounts. Mix them in rather than dumping a whole filter in one spot.
Always bury food under at least 1 to 2 in (3 to 5 cm) of bedding. Exposed food draws fruit flies. Rotate feeding spots around the bin so you can see which areas have finished.
Where to keep the bin
Worms are comfortable at roughly 55 to 77°F (13 to 25°C). Inside that range they eat and breed well. Outside it, they slow down.
- Below about 50°F (10°C), feeding slows sharply. Near freezing, worms can die.
- Above about 85°F (29°C), they get stressed. A bin in direct summer sun can kill them in an afternoon.
Kitchens, basements, laundry rooms, garages in mild climates, and shaded balconies all work. Keep the bin away from radiators, ovens, and sunny windows. If you keep it outdoors, move it inside or insulate it before hard frosts. The winter composting guide covers cold-weather options.
How to harvest worm castings
Harvest when most of the bin looks like dark, crumbly soil and you cannot pick out the original food or bedding. That usually takes 3 to 6 months after setup. Two methods do most of the work for you.
Migration method
- Push all the finished material to one side of the bin.
- Add fresh damp bedding and food to the empty side only.
- Wait 2 to 4 weeks. Most worms move over to the food.
- Scoop out the finished side and refill it with new bedding.
Stacking bins work on the same idea. You add a new tray with food on top, the worms climb up through the holes, and the bottom tray empties of worms.
Light method
- Dump the bin contents onto a tarp in bright light.
- Rake them into several cone-shaped piles.
- Wait 10 to 20 minutes. Worms burrow down away from the light.
- Scrape off the top layer of castings. Repeat until each pile is mostly worms.
- Return the worms to the bin with fresh bedding.
This takes an hour or so but gets you castings the same day. Castings are strong and fine. Mix them into potting soil at about 1 part castings to 4 parts mix, or top-dress houseplants with a thin layer. The guide to using compost has more options.
Troubleshooting a worm bin
Most worm bin problems come from too much food or too much water. The fix is nearly always the same: stop feeding, add dry bedding, and wait.
| Problem | Likely cause | Fix |
|---|---|---|
| Sour or rotten smell | Overfeeding, too wet | Stop feeding for 1 to 2 weeks, add dry shredded paper, remove any rotting clumps |
| Worms crawling up walls or out | Too wet, too acidic, or new bin | Add dry bedding and crushed eggshells, leave a light on overnight |
| Fruit flies | Exposed or fermenting food | Bury food deeper, add a layer of dry paper on top, freeze scraps first |
| Worms thin or dying | Too hot, too cold, too dry, or starved | Check temperature and moisture, move the bin, feed lightly |
| Food not disappearing | Too much food, too cold, or too few worms | Feed less, move somewhere warmer |
| Tiny white worms or mites | Very wet or acidic bin | Usually harmless; dry the bin out and add eggshells |
| Pool of water at the bottom | Poor drainage, wet food | Clear holes, add bedding, cut back on melon and other watery scraps |
For smells in any kind of compost, see why does my compost smell.
Next step
If you live in a small space, compare a worm bin with the other options in composting in an apartment. If you want to handle meat and dairy too, look at bokashi composting, which pairs well with a worm bin.
Frequently asked questions
Can I use earthworms from my garden in a worm bin?
No. Garden earthworms live deep in soil and do poorly in a shallow bin of food scraps. Use red wigglers (Eisenia fetida), which live in the top layer of rotting material and eat and breed fast in a bin.
How many worms do I need to start?
About 1 lb (roughly 450 g) of red wigglers is a common starting amount. As a rough rule, that handles about 0.5 lb (225 g) of food scraps a day once the bin is settled. Start with less food than that and build up.
Does a worm bin smell?
A healthy worm bin smells like damp forest soil. A sour or rotten smell almost always means overfeeding or too much moisture. Stop feeding for a week and add dry shredded paper. See why compost smells.
Can worms escape from the bin?
A few will wander, especially in the first days or when conditions go wrong. A light left on over the bin for the first few nights keeps them down. Mass escapes usually mean the bin is too wet, too acidic, or too hot.
What do I do with my worms when I go on vacation?
Worms can go 2 to 4 weeks without feeding. Before you leave, give them a normal feeding with extra fresh bedding on top, and keep the bin out of direct sun and heat.
Can I put citrus and onions in a worm bin?
In small amounts. Citrus peels and onions and garlic are fine in an outdoor pile, but worms tend to avoid them and they can make a small bin acidic or smelly. Feed them sparingly or send them to a backyard pile instead.
How long before I get usable worm castings?
Roughly 3 to 6 months after setup, depending on temperature and how much you feed. The bin is ready when most of it looks like dark, crumbly coffee grounds and you cannot recognize the food or bedding.