Vermicompost refers to worm compost created in about three months by a colony of worms such as the red wiggler (Eisenia fetida), kept in an enclosed bin with appropriate food and bedding.
Home hobbyists setting up their first worm bin or farm will notice occasional specks of black worm manure soon after their worms become active. This dark material becomes denser and denser as worms continue to eat about half their weight daily, creating vermicompost.
The end result of composting with worms results in an earthy-smelling, black granular product called vermicompost. Technically, vermicompost may contain some incomplete organic wastes such as kitchen scraps and shredded paper or cardboard bedding.
The term worm castings, often used synonymously, actually refers to a purer grade of worm droppings or manure screened to remove incompletely degraded organic matter. The phrases worm humus and worm manure can be used to refer to either vermicompost or worm castings.
Nearly pure castings will resemble coffee grounds, being dark brown in color. Typical vermicompost also resembles coffee grounds but with occasional lumps of rotting food or pieces of bedding scattered throughout. The smell of either should be pleasantly earthy, like a garden after it rains. Any sour or rotten smell indicates that the compost worms need more time to complete their digestion of the vermicompost components.
High-quality vermicompost can be obtained by using a flow-through bin that permits scraping of a breaker bar across a grate at the bottom to remove finished castings while leaving incomplete castings, worm eggs and the worms themselves free to continue the vermicomposting process closer to the surface of the worm bin or bed. For those in rural areas, composting with horse, cow or rabbit manure also results in a rapidly finished vermicompost with high-quality nutrients, according to Glenn Munroe of the Organic Agriculture Center of Canada.
Vermicomposting provides a greater benefit to plants than regular compost, as the worm's gut adds beneficial bacteria and concentrated but gentle-for-plants minerals to the original organic raw material.
No standards exist to dictate what percentage of worm castings has to be present in order for a product to be 100 percent pure, according to Bentley Christie, who operates the website RedWormComposting.com. Ways to accurately measure the castings percentage have not been developed, he notes. Quality vermicompost can be ascertained only by the look and feel of the material, the reputation of the company making it and its ability to promote plant growth, he writes.