Worm castings
Also known as Vermicompost, Vermicast, Worm compost
In short
Worm castings are the droppings of composting worms, and vermicompost is the mix of castings and partly processed organic matter. They are a gentle, nutrient-rich amendment with high microbial activity, used in modest proportions in potting mixes.
How it looks
Dark brown to black, fine, crumbly granules with an earthy smell, damp like a wrung-out sponge when fresh. Vermicompost may still contain bits of undigested food or bedding. Most is made with the red wiggler worm Eisenia fetida.
Signs
Too much castings in a pot can over-fertilise. Fresh, uncured vermicompost may still be acidic; curing for up to three months lets acids neutralise.
What favours it
Microbial activity in castings can be 10–20 times higher than in the material the worms ate. Vermicomposting tends to increase available nitrogen and phosphorus.
Prevention
- Use castings as a portion of the mix, not the whole; to avoid over-fertilising, Wikipedia notes advice to mix them no more than equally with potting soil.
- Let home-made vermicompost cure before use.
- Balance castings with drainage materials such as perlite or bark.
Treatment
Start with the first step and move down only if the problem persists.
- If a pot stays wet after adding castings, repot with more coarse material.
Pros and cons
Pros
- Adds nutrients in a gentle form.
- High microbial activity and enzymes that can support root growth and germination.
- Made from recycled food and garden waste.
Cons
- Can over-fertilise if used undiluted or in large amounts.
- Home-made vermicompost needs curing, up to about three months, before use.
Look-alikes
- Compost
- Compost is coarser and more variable; castings are finer and more uniform.
Typical uses
Vegetables, herbs, houseplants and seedlings as a small part of the mix or as a top-dressing; not for carnivorous plants.
Related
Sources
Written in our own words from these sources. Check a product label before using any treatment.