Worms are remarkable composters. Various kinds of earthworms find their way into any compost pile in contact with bare soil. They work their way around the outer areas of the pile, consuming organic material and processing it through their bodies. In a passive pile of leaves, the worms do as much work as microorganisms in the year or two it takes to turn the pile into compost. When organic waste is left on the soil surface, earthworms are involved to a large extent in breaking the waste down and pulling it into the soil.

You can use worms as a composting tool. Add worms to a pile outdoors, or set up a worm box to handle kitchen waste. Be sure to distinguish between ordinary earthworms and composting worms, which are highly specialized for composting duty but don’t usually survive elsewhere.

Earthworms perform valuable services in the compost pile. Their castings constitute a superior nitrogen-rich fertilizer—the more earthworms in a compost pile, the richer the finished compost. Earthworms secrete calcium carbonate, a compound that helps to moderate soil pH. As earthworms move around a pile, they rearrange and loosen the compost materials, improving aeration. Their tunnels provide a way for other organisms, such as sowbugs and millipedes, to get deep into the pile. Like earthworms, these organisms contribute to the decomposition process.

Composting worms—known variously as red worms, red wigglers, red hybrids, and manure worms—reproduce much more rapidly than common earthworms. They process more organic material than earthworms simply because they multiply so quickly. It takes just 8 red worms to produce 1,500 new red worms in only six months. Since they don’t usually survive in the home landscape, however, they must be purchased each season. Two types of composting worms are commonly sold: Eisenia foetida can’t live in the soil at all, and Lumbricus rubellus can sometimes survive in the soil. A pound of red worms (about 1,000 to 2,000 worms) typically costs between $15 and $30.

Worms in a compost pile

Worms are useful in helping to speed up decomposition in any compost pile, although obviously they aren’t practical in piles that are run through a shredder. They’re most valuable in passive compost piles that are just left alone to rot. Either earthworms or composting worms can cut the decomposition time of a passive pile by at least 50 percent.

Composting worms are much more efficient than common earthworms. One pound of composting worms added to a compost pile in late spring can make a noticeable difference in the speed of decomposition. Unfortunately, composting worms are so voracious that they literally eat themselves out of work. Once they digest most of the organic material in the pile, they’re in danger of starving to death. To keep the worms going, transfer them to a fresh pile of organic waste promptly.

Unlike earthworms, composting worms stay above the soil and don’t hibernate. Therefore, they usually die if they’re left in a pile during the winter in the North. If you want to protect composting worms, devise a holding box for them in the basement, garage, or other location where the temperature stays above freezing.

Worm boxes

Although raising ordinary earthworms in the home is difficult, composting worms are suited to life in a box. Some people keep a worm box the year around to process the family’s kitchen waste, including meat scraps. Others simply use a worm box to hold composting worms during the winter so that they can form the nucleus of a new population for the outdoor compost pile in spring.

Composting worms prefer a temperature range of 55 to 77 degrees, making a heated basement, garage, attic, or sunroom a likely site for the worm box. In mild-winter climates, the box can probably stay outdoors all year, but be sure to bring it indoors if you expect a cold snap. A properly managed worm box won’t smell or attract insects. However, if conditions get out of balance, flies may appear or odors may develop. As this section will explain, the problem disappears when the factors are brought back into balance.

Your first step in planning a worm box is considering its size and shape. The size depends on how much waste you intend to process. The rule of thumb is to provide roughly 1 square foot of surface area for each pound of food waste produced per week—for example, 7 pounds of kitchen scraps per week requires about 7 square feet of surface area, or a box about 2 by 3 1/2 feet. The container should be from 8 to 12 inches deep to avoid compaction.

The number of worms in the box determines how much waste you can process. About 2,000 composting worms (roughly 2 pounds) can process 7 pounds of kitchen scraps in a week. Two pounds of worms for every pound of waste per day is a standard ratio. If you generate about 1/2 pound of kitchen waste daily, then 1 pound of worms should be sufficient to do the job. Remember, composting worms multiply quickly to cover any increase in waste.

The worms need an organic bedding material, such as shredded leaves, newspaper, cardboard, or peat moss. Add a few handfuls of garden soil to the bedding mix to introduce microbial decomposers to the box. As the bedding material decomposes along with the kitchen waste, it will become dense and air access will decrease proportionally. You may have to add bedding material to ensure that the worms get enough air.

To survive, composting worms need an environment consisting of about 75 percent moisture. Weigh the bedding material, then mix it with water equal to three times that weight. If you have 4 pounds of bedding material, then add 12 pounds of water. Since 1 pint of water weighs 1 pound, that means adding 12 pints, or 1 1/2 gallons, of water. Thoroughly moisten the bedding material before adding the worms.

Most worm farmers cover the worm box with a sheet of black plastic or a wooden cover to keep in moisture and keep out light. Follow a pattern in adding kitchen waste; once you have deposited material to a particular spot, don’t disturb that area with new waste for about a month. Chopping the waste is unnecessary, but it’ll break down faster if you chop it. Some people chop the scraps in a blender, drain off the liquid, and add the solids to the worm farm. Whenever you add waste, chopped or not, cover it with bedding material.

Every two to four months, renew the worm box by adding new bedding and removing some or all of the finished compost. The easiest method of doing this is to remove one half of the material, including the worms, and spread it out in the landscape as compost. The worms will die, contributing further to the compost. Use fresh bedding material to fill the space made available by removing the finished compost from the box. If you don’t add any new waste to the old bedding material, the worms will migrate to the new bedding in three to four weeks. Then you can remove the other half of the old material, including any worms lagging behind, and replace it with new bedding. The worm farm is now good for another few months.

Another method is to separate the worms from the bedding by exposing the worm box to light. The worms will move toward the bottom, away from the light. As you scoop off the composted material in top of the box, the worms will collect in an even tighter group on the bottom. Add fresh bedding after you remove the compost.

If you keep the box indoors through the winter, move it to a shady, protected spot outdoors in spring. As an alternative, dump the worms onto the compost pile and set up the worm box again in fall.