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Vermicomposting: Let the Worms Do the Work

Vermicomposting is an advanced form of composting. It involves a relatively small bin that is not open to the ground. The bin contains worms that rapidly convert table scraps and garden debris into rich compost. This allows apartment and condo dwellers with small or container gardens to reap the benefits of making their own compost.

Red wigglers and brandling worms are the most common species used in vermicomposters. They can often be found in a standard compost bin and are adventurous enough to wander into manure piles, while regular earthworms disdain compost and manure and pretty much stick to regular soil. The red worms eat organic matter, which passes through their system. Their manure is often called castings and is finished compost.

Making a Vermicomposter

In planning on making a vermicomposter, first take into consideration the size of the area in which it can be located. Normally, it should be placed in an area that is easy to access, but also not near places with carpeting where spilled compost or table scraps could be a problem. The bin can be made from wood or plastic. It should be relatively shallow; more than 12 inches deep is not recommended as the red wiggler worms are top feeders and the compressed waste can begin to rot at greater depths. An NMSU pub recommends that one square foot of surface area be provided per pound of waste1.

Wood is the preferred material for building a vermicomposting bin because it usually provides better aeration and moisture control. However, refrain from using redwood or cedar, natural chemicals within these woods can actually kill the worms. Holes should be drilled in the bottom and sides of the bin to allow in air and out water. For this reason, the bin should be placed in a plastic container to catch any run-off. The bin also needs a lid to keep conditions dark (worms like the dark) and to help control moisture. Outdoor bins will need to be insulated during the winter season to protect the worms.

Getting Started

Put a generous layer of bedding materials (about 3/4 to the top of the bin) in the bottom of the bin. Bedding materials can be made up of straw, hay, sawdust, old shredded newspapers, or shredded cardboard. If grass clippings are to be used, allow them to thoroughly dry out and brown slightly. These materials should not be packed down. Dampen the materials, wait a few days to ensure the materials are not heating up from excessive aerobic decay. Then add worms. A couple handfuls of worms can be gotten from a neighbor's compost pile or are available from dealers and some gardening centers.

Generally, it takes about two pounds of worms (about 2000 of them) to process one pound of table scraps per day. They will also need about 4 cubic feet of space. The worms are continually reproducing. So it is possible to start out with a limited number and allow their population to reach equilibrium. (Remember, don't use regular earthworms - use the red ones.)

Feeding the Worms

Worms can eat an incredible amount of organic materials, including most table scraps (excluding meat and dairy), coffee grounds, and grass clippings. The worms are not fond of garlic or raw onions, or hot spices. Too much citrus can make the compost too acidic, ground eggshells will cure this problem. Be sure to add a bit of sand now and again. The worms use the abrasive stuff to aid in digestion. Avoid plants that have been sprayed with insecticides or herbicides or poisonous plants such as the leaves of rhubarb or the flowers of wisteria. Add table scraps by pulling back the pile and placing them beneath the surface - this will help keep insects and other unwanted pests from invading the bin.

Getting the compost

When all of the bedding has disappeared in two or three months, it is time to take out some or most of the compost. The easiest way to do this is to push all of the current compost over to one side of the bin. On the other side add new bedding and compost. Give the worms a couple of days to move over to the new food. Then remove the finished compost and add additional bedding and food to the other side as well. A screen can also be used to separate the worms from the compost by sifting (3/4 inch screen works best). Bright lights can also used to drive the worms down into the pile and successive layers of compost removed.

The compost is ready for use.

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  1. New Mexico State University

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