Vermicomposting

21 January 2008

Virginia Cooperative Extension, Charlottesville/Albemarle County Office
460 Stagecoach Road, Charlottesville, Virginia 22902
phone: 434.872.4580   fax: 434.872.4578

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Every home kitchen generates food scraps for disposal. Throwing these scraps in the garbage can create odor problems and adds to the volume of waste going to the landfill. A viable alternative to disposing of food scraps in the landfill or the sewer system is to compost them.

Composting is a process by which organic materials are converted from an unstable product, which is likely to further decompose and create objectionable odors, to an increasingly more stable product that will store well without being offensive. A diverse population of microorganisms and invertebrates, called decomposers, performs this process. Most people think of composting as a pile of organic materials that slowly decomposes and creates heat. This is called thermophilic composting because it relies primarily on high-temperature tolerant microorganisms. Another form of composting is called vermicomposting.

In vermicomposting, the primary agents of decomposition are worms. They convert raw organic wastes to a nearly stable humus-like material. The main process by which organic materials are converted occurs as the wastes pass through a worm's gut and are digested by the worm. Worms stir and aerate the waste pile, so that turning is not required. Worms can stabilize organic materials faster than microorganisms because they grind the material, thus increasing its surface area and speeding decomposition by microorganisms. Material that actually passes through the gut of a worm is called castings.

Successful vermicomposting requires a worm bin that provides the appropriate environmental conditions for worms. Worms breathe through their skin and require an environment that is moist, but not so wet that they drown. The material in which they live should feel like a damp sponge and release a few drops of water when squeezed.

Various worm species have different temperature requirements. Eisenia fetida, the one recommended for a composting worm bin, can survive at temperatures between 35 and 100F but performs best between 65and 78F.

Worms do not have eyes, but they do have light receptors on their skin. They do not like light, and will quickly dig down into a bin to avoid it. For this reason, it is a good idea to provide a cover for your worm bin.

You can purchase a worm bin or you can build your own. A good rule of thumb for sizing a worm bin is this: you can process one-half pound of food scraps per day for each square foot of worm bin surface area. For example, a bin that is 18 inches by 24 inches (18/12 x 24/12) is 3 square feet in surface area and can process about 10.5 pounds of food a week (3 sq ft x 1/2 lb/ft sq/day x 7 days/week = 10.5 lbs).

A worm bin must be open enough to allow for good aeration. The bin should include a cover to minimize the attraction of fruit flies and other pests, but if a plastic lid is used, be sure and drill holes in it so air can get in. Bins can be made of a variety of materials--wood and plastic are common.

Place a six- to eight-inch layer of bedding material in the bin. Paper shredded into two-inch or narrower strips, including office paper and newspaper, cardboard, and well-composted horse or cow manure all make good bedding. Moisten the bedding material by soaking it in water, then drain it and squeeze out the excess moisture and fluff up the material to assure that it is well aerated.

Add one-half to one pound of worms for each square foot of surface area of worm bed. Give the worms time to burrow into the bedding material before you feed them. To discourage worms from leaving the bed, it is a good idea to leave a light on near the bin the first few days.

Worms can process a wide range of organic materials as long as the materials are not too salty or too acidic. Fruits, vegetables, coffee grounds and filters, and tea bags all make good worm food. Citrus fruit and peels should only be applied in small amounts because of their high acidity. Meat, bones, dairy products, fatty or greasy foods, and pet manure should not be placed in worm beds due to odor and pathogen concerns.

To feed the worms, bury the food in clumps, putting each feeding into one small space within the bin. Feeding once or twice a week is recommended. The bin should remain covered with the cardboard except when you are feeding. A new layer of moist bedding three to four inches thick should be placed on top of the bin about every two months.

Harvesting the Vermicompost: Every three to six months or when the bin begins to fill, the worms should be separated from the vermicompost if your objective is to generate more worms. Remove the worms from the vermicompost relatively early (after two to three months), and divide the worms into new bins. Giving the worms extra room will encourage high reproductive rates.

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For more information about this and other landscape topics contact your local Virginia Cooperative Extension office. The local Virginia Cooperative Extension office numbers are Albemarle 872-4580, Fluvanna 591-1950, Greene 985-5236, Louisa 540-967-3422, and Nelson 263-4035.