Composting with Worms

By Matthew Werner

Vermiculture means using earthworms to decompose organic matter. Vermi is the Latin word for worm-like, as in vermicelli. The end product of vermiculture is a rich soil amendment made up of earthworm casting and earthworm biomass.

Earthworm castings include soil mixed with partially digested organic matter, plus a large bacterial population. Because of the active bacterial component, the organic matter in the castings continues to decompose, releasing nutrients like nitrate, ammonium, and phosphate, and much of the organic matter is transformed into humus. Earthworm casts also contain hormones that stimulate plant growth. Many developing countries (India, Cuba and Kazakhstan are examples) use vermicastings as a primary fertilizer, where it is typically thought to be superior to thermophilic compost as a fertility amendment.

The earthworms most commonly used in vericulture are called Eisenia foetida (also known as the redworm, manure worm, brandling worm or tiger worm). This species thrives with access to a low of raw organic matter. It is also a prolific breeder: given ideal conditions, a pound of redworms can produce 100 pounds of redworms in one year. Harvested earthworms can be used to decompose more fresh organic matter, or they can be sold to other vermiculture operations. The resulting earthworm biomass from vermiculture could potentially be used as animal feed as well, because it is very rich in protein (60-70% on a dry weight basis), and contains a more favorable array of amino acids than other meat and fishmeal protein sources for livestock feed.

In California, vermiculture is currently used mostly on the home scale to process kitchen and yard wastes. Schools and businesses are also getting in on the act, using vericulture to process food wastes. However, we are beginning to see large scale uses of this technology as cities struggle to divert 50% of waste from landfills by the year 2000, as mandated by California law AB939, which went into effect in January 1990.

The Worm Concern, established in 1976, is a good example of how a commercial vermiculture operation can help address the state's growing waste disposal problem. This Simi Valley business currently takes in more than 70 tons of yard waste per day, grinds it up, and feeds it to earthworms. The yard waste includes leaves, grass clippings, brush, tree trimmings, weeds, and manure. The company sells a variety of soil mixes, starting at $14 a yard. Pure vericompost costs $100 per yard.

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Matthew Werner has a Ph.D. in soil ecology. He is the resident earthworm expert at the Center for Agroecology and Sustainable Food Systems at U.C. Santa Cruz.