What kind of worms are used for vermicomposting?

Most worm farms raise two main types of earthworm: Eisenia foetida and Lumbricus rubellis. These worms are commonly used to produce vermicompost, as well as for fish bait. Both are referred to by a variety of common names, including red worms, red wigglers, tiger worms, brandling worms, and manure worms. These two species are often raised together and are difficult to tell apart, though they are not believed to interbreed. While several other species have been successfully bred in recent years, this fact sheet focuses primarily on the use of these species.

The night crawler (Lumbricus terrestrius) is also harvested and sold for fishing bait. This species does not breed well in captivity and is generally harvested from wild stock.

What do worms need?

Worms can survive a wide variety of temperatures, but they thrive best at temperatures between 55 and 77 degrees Fahrenheit (13-25 degrees Celsius). They need a moist, organic substrate or "bedding" in which to live. They will eat the bedding and convert it into castings along with other feed. While moisture is vital, so is oxygen, and bedding should be about as damp as a wrung-out sponge. A worm's skin is photosensitive and they prefer a dark environment.

Because worms have no teeth, they need some type of grit in their bedding that they can swallow and use in their gizzard to grind food, much like birds do with small stones. A little soil or sand will work, but it should be sterile so as not to introduce foreign organisms. Common additives used include rock dust or oyster flour (ground up oyster shells).

Since oyster flour is basically calcium carbonate, adding too much will raise the pH in the worms' environment. Worms prefer a slightly acidic pH level of about 6.5. For a typical worm bin, no more than a tablespoon of grit is needed, which should not significantly alter the pH.

What will worms eat?

Worms will eat a wide variety of organic materials such as paper, manure, fruit and vegetable waste, grains, coffee grounds, and ground yard wastes. While worms will eat meat and dairy products, it is best not to feed these materials or oily foods to worms, due to potential odor and pest problems. Worms will consume limited amounts of citrus wastes, but limonene, a chemical compound found in citrus, is toxic to worms, so it is best to limit or avoid feeding them this material.

Since worms have no teeth, any food they eat must be small enough to swallow, or soft enough for them to bite. Some foods may not be soft enough initially for them to consume, but they quickly degrade so that the worms can consume them.

Where should you keep worms?

Worms can be raised on a small or large scale, depending on your goals. If you are trying to manage food scraps for yourself or your family, a small 12 to 20 gallon worm bin should be adequate. The bin should be dark and opaque, and it should have a lid and drainage and aeration holes in the bottom. Small 1-inch legs and a tray underneath are also helpful.

If you are trying to manage larger amounts of organic materials or produce large amounts of worms or vermicompost, worms can be managed in low-mounded rows called worm beds or "ricks," or in large in-vessel continuous-flow systems available from suppliers. Worms burrow into the bedding to protect themselves, and they will not come into sunlight unless bedding conditions are intolerable.

How do you harvest worms and vermicompost?

Large-scale worm farmers using worm beds generally use harvesting equipment to separate worms and castings. In-vessel "continuous flow" systems are generally designed to produce vermicompost. They rely on the surface-feeding tendency of red worms to incorporate a casting harvest mechanism on the bottom of the system, below the active feeding area. Food and additional bedding is added to the top, encouraging the worms to continue feeding upwards.

Smaller scale worm bins are harvested in a variety of ways. In all cases, harvesting should begin when the bedding and consumed food has turned a rich dark brown, with a consistency of coffee grounds. Waiting longer can result in a sludgy material that is difficult to harvest and may become anaerobic and begin to smell.

One commonly used method of harvesting is to dump the bin onto a tarp in bright light, allowing the worms to burrow down to escape the light. Castings can then be separated by slowly scraping them away, pausing periodically to let the worms burrow further. Eventually, you are left with a pile of worms.

Some will harvest by placing new bedding in one half of the bin, and feed exclusively on that side. Eventually (sometimes over a period of several weeks) most of the worms will move to the side with the new bedding, and the finished compost can be harvested.

One simple method is to place a large amount of food in one area of the bin. Within a few days to a week, this should become a writhing mass of feeding worms. By turning a plastic bag inside out over your hand, you can then "reverse harvest" the worms by simply grabbing the mass of worms and turning the bag right-side out. You then have enough worms to start your bin again. Some worms and egg cases will be left in the castings. This should be no problem if the castings are used soon for indoor potted plants.  Castings should be cured before outdoor use.

Harvested castings can be mixed into potting soil soon after harvest for best effect on indoor plants. If they are to be stored or used for outdoor plants, they should be cured in an aerobic environment to dry, eliminate the potential to introduce new species and prevent mold.

Where can I get worms or worm bins?

To inform people where worms and bins can be procured, the CIWMB maintains a list of worm and worm bin suppliers at www.ciwmb.ca.gov/Organics/Worms/WrmSuply.htmand http://www.ciwmb.ca.gov/Organics/Worms/BinSuply.htm. Some larger equipment suppliers can be found listed with other in-vessel composting technologies at www.ciwmb.ca.gov/FoodWaste/Compost/InVessel.htm

Will I need to buy more worms?

space, moisture, pH, temperature, bedding material, and amount of food, among others. A typical household worm bin might start out with one pound of worms (approximately 1,000 adults), which will soon multiply to 2,000-3,000 if conditions are good. Conversely, if one or more of the above conditions are unacceptable, the worms may "crawl" (leave the bin) or die off.

Red worms are hermaphroditic, meaning that each individual has both sexes, but they need two worms to procreate and exchange DNA. A small egg case, usually amber in color, is produced which can contain from 2 to 20 baby worms.