Learn / Composting methods
Vermicomposting: let worms make your compost.
Composting worms eat organic waste and leave behind fine, dark, crumbly castings that seedlings love. It works in a small bin at home or a large bed on a farm, and it suits nurseries and high-value crops.
What to expect
Vermicompost is best seen as a premium soil and seedling input, made in small quantities, rather than a way to produce large volumes of compost for a whole farm.
Which worms to use
Use composting worms, which live in rotting organic matter and eat it quickly. These are different from the burrowing earthworms you find deep in garden soil. Species suited to East Africa include:
Tiger worm
Eisenia fetida. Small (under 10 cm), hardy, and the species most commonly used for vermicomposting in Kenya.
African nightcrawler
Eudrilus eugeniae. Larger, up to about 20 cm, and best adapted to subtropical climates.
Perionyx excavatus
Another composting species listed for tropical conditions.
Highland forest earthworm
A pigmented Kenyan highland forest earthworm is reported to produce a finer vermicompost.
To get started, ask a farmer or supplier who already keeps worms for a few handfuls of worm-rich bedding, rather than collecting worms from the wild.
SOURCES: KALRO LOW-COST COMPOSTING TECHNOLOGIES PAMPHLET; CIRAWA VERMICOMPOSTING HANDBOOK
Keep them cool, dark and damp
- Temperature. Worms do best between 15 and 25°C. Much of the Kenyan highlands falls in or near that range. In hot lowlands, siting and shade matter a lot, because temperatures above 35°C kill worms.
- Darkness. Worms avoid light. Keep the bed shaded and covered.
- Moisture. Keep the bedding consistently moist. The handbook gives about 80% as ideal. Use enough water to keep it moist without making it soggy or waterlogged. Worms survive in drier conditions, but they work much more slowly.
- Acidity. Worms prefer neutral conditions and tolerate a pH of about 5 to 9.
- Site. Choose a shaded spot near water and close to your waste, on slightly sloping ground so excess water drains away.
Small systems fail fast.
The handbook warns that feeding mistakes, too much or too little water, lack of shade, or a heat wave can quickly collapse the worm population in a small system. Look in now and then to check that the worms are present and active.
SOURCES: CIRAWA VERMICOMPOSTING HANDBOOK; KALRO PAMPHLET
A simple bed, step by step
This follows the bed method described in the KALRO pamphlet for Kenyan farmers.
- Build the bedMake a base of concrete, wood or plastic sheeting, with walls 20 to 30 cm high from wood, logs or stone. Place a wooden board on the base, topped with chicken wire, so air can reach the bedding and you can lift it out.
- Lay a coarse layerSpread a 10 to 15 cm layer of coarse material such as banana trash, maize stover or coffee husks. Don’t use poultry droppings, which harm worms.
- Add a fine layerAdd coarse manure from cattle, pigs, sheep or goats. You can also use grass clippings, threshed beans, maize bran or brewery waste. Give fresh manure time to age or pre-compost for about 15 to 20 days before feeding it to worms.
- Wet everythingWet all the materials thoroughly, with no dry patches.
- Add the wormsPlace the worms in clusters, as small handfuls of worm-rich material, in holes about half a metre apart. This is easier on the worms than handling them one by one.
- CoverCover the bed with banana leaves or dark polythene sheeting. Add fresh layers of food as the worms eat the older ones.
- Look after itCheck moisture regularly. Shake the chicken wire firmly now and then to scare off predators.
For a household.
A single container or a stack of trays works, with a bottom tray to catch excess liquid. A 250-litre drum or plastic container with air holes, placed in shade, has also been used. Start with a few handfuls of waste and don’t overload it.
SOURCES: KALRO LOW-COST COMPOSTING TECHNOLOGIES PAMPHLET; CIRAWA VERMICOMPOSTING HANDBOOK; CONTAINER COMPOSTING (KUMASI, GHANA)
What worms eat, and what they don’t
Good feed
- Aged or pre-composted cattle, goat, sheep or pig manure
- Banana trash, maize stover and cereal straw
- Coffee husks and residues
- Leaf litter and green waste
- Grass clippings, threshed beans, maize bran
Avoid
- Poultry droppings
- Anything with heavy metals or other pollutants
- Too much protein, such as meat or large amounts of rich waste
- Large, woody or coarse pieces. Cut or shred to under about 2 to 3 cm
Pre-compost the feed first.
Soft, moist, partly broken-down material is best. The handbook suggests pre-composting feed for about 15 to 20 days, with a carbon-to-nitrogen ratio of about 20 to 30. A well-fed worm can process about its own body weight in waste each day.
Testing a new feed
Before switching a whole bed to a new material, put about 50 worms in a small box of it. If two or more have died after 24 hours, the material needs more pre-composting first.
SOURCES: CIRAWA VERMICOMPOSTING HANDBOOK; KALRO PAMPHLET
Collecting your vermicompost
The sources give different timings: roughly 6 to 12 weeks in one part of the KALRO pamphlet and 3 to 6 months in another. It depends on your worms, feed and temperature. Judge by the product: fine, black and consistent.
- Stop feedingWithholding feed for about three weeks gives a finer, more uniform product.
- Draw the worms offPlace fresh fine feed, such as wheat bran, brewer’s waste or fresh dung, in a new spot or on a screen to attract the worms to it.
- Collect what is leftSpread the compost out to dry in the sun and pick out any remaining worm pockets by hand. Surplus worms can go back into the bed, feed fish or poultry, or start a new bed.
- Sieve and matureSieve the compost through a 5 or 10 mm mesh. Let it mature for 25 to 30 days after the worms are removed, drying it to 40% moisture or less.
Using it
| Use | Guidance |
|---|---|
| Seedlings and potting mix | Vermicompost is the main component of seedling and potting media. |
| Field crops | Typically about 2 tonnes per hectare. |
| Demanding horticultural crops | Up to about 8 tonnes per hectare. |
| Fertilizer savings | It can cut synthetic fertilizer use by 25 to 50%. Under organic systems it may be the only fertilizer. |
| Vermicompost tea | Mix 1 part vermicompost with 10 parts water and aerate it for 24 to 72 hours with a simple pump. The liquid that drains from the bed also needs aerating before use. |
SOURCES: KALRO LOW-COST COMPOSTING TECHNOLOGIES PAMPHLET; CIRAWA VERMICOMPOSTING HANDBOOK. THE CIRAWA RATES COME FROM A EUROPEAN HANDBOOK, SO CHECK THEM AGAINST YOUR SOIL TEST AND CROP.
Common problems
| Problem | Likely cause | Fix |
|---|---|---|
| Worms dying or leaving | Too hot, too dry or too wet, poor feed, or overfeeding. | Move the bed into shade, adjust moisture, stop feeding unsuitable material, and feed less. |
| Predators eating worms | Birds, chickens and other animals reach the bed. | Cover the bed with chicken wire and shake it now and then. |
| Bed turns putrid | Overloaded or too much wet feed. | Stop feeding, remove the excess and let the bed recover. |
| Slow production | Too few worms, cold or hot conditions, or dry bedding. | Check the temperature and moisture, and count the worms now and then. |
SOURCES: CIRAWA VERMICOMPOSTING HANDBOOK; KALRO PAMPHLET; CONTAINER COMPOSTING (KUMASI, GHANA)
Questions people ask
How many worms do I need?
For a small bed, a few handfuls of worm-rich material is enough to begin. The population grows. One handbook describes a commercial system starting at about 5,000 worms per square metre and reaching about 20,000 per square metre within three months under good conditions.
Can I use poultry manure?
Not fresh, and not as bulk feed. The KALRO pamphlet says poultry dung is harmful to worms.
Does it smell?
A healthy bed smells earthy. A sour or rotten smell means it is too wet or has been overfed.
Can I sell the worms?
Surplus worms can be sold, used as fish bait or poultry feed, or used to start new beds elsewhere.
Is vermicompost better than ordinary compost?
It is finer and well suited to seedlings and potting mixes, but it is produced in smaller amounts. Many growers use both: ordinary compost to build soil across the farm, and vermicompost for nurseries and high-value crops.
Want help starting a worm bed?
We train farmers, schools, nurseries and institutions to set up and run worm beds and other composting systems.