Organic materials make up approximately two-thirds of the waste stream. While much of this is paper which can be used more efficiently or recycled, a large portion is material like food waste for which few beneficial options outside of composting exist. Fortunately, nature has provided one option that has been receiving increasing attention–vermicomposting.

So what, you may ask, is vermicomposting and how does it work? Well, “vermi” is the Latin word for worm, and worms like to feed on slowly decomposing organic materials (e.g., vegetable scraps). Vermicompost, or castings, is worm manure. Worm castings are considered by many in horticulture to be the very best soil amendment available. The nutrient content of castings is dependent on the material fed to the worms–and worms are commonly fed materials with high nutrient content, such as food waste and manures. The biology of the worm's gut facilitates the growth of fungus and bacteria that are beneficial to plant growth. In addition, many chemical compounds are found in castings that are thought to promote plant growth.

The essential components of a home vermicomposting unit are an aerated container, some moist bedding, food scraps, and a few thousand red worms  or red wigglers (Eisenia foetida).

The worms: Mary Appelhof, author of “Worms Eat My Garbage” recommends two pounds of worms — about 2,000 wigglers — for every pound per day of food waste. To figure out how much food waste your household generates, monitor it for a week and divide by seven. Note: Some vermiculture experts advise starting out with a smaller amount of worms, which isn't a bad idea if you are relatively new to all of this. Of course, you'll have to reduce the amount of food scraps you put in the bin, until the population increases. One pound of redworms will easily take care of each half-pound of garbage. To add worms to the bin, simply scatter them over the top. The skin on the worm reacts to light and they will immediately work their way down into the bedding to get away from the light.

The bin: You can purchase a vermicomposting bin or make your own. Depending on how much food waste your house generates will depend on the size of the bin. A simple internet search will yield lots of worm bin results but here is one for a larger wood bin and one for aplastic bin made out of tote boxes. The container depth should be between eight and twelve inches. Bins need to be shallow because the worms feed in the top layers of the bedding. A bin that is too deep is not as efficient and could potentially become an odor problem.

When beginning a vermicomposting bin, start by adding moist bedding — things like shredded paper, dead leaves and other materials high in carbon (it's should mimic the worms' natural habitat, in dried leaves on a forest floor) — into the bin, and add the worms to their new home. Bedding is the living medium for the worms but also a food source, so it should be moist (something like a wrung-out sponge) and loose to enable the earthworms to breathe and to facilitate aerobic decomposition. Other common bedding materials can be used including newspaper, sawdust, hay, cardboard, burlap coffee sacks and peat moss.

Most vermicomposters avoid using glossy paper from newspapers and magazines, junk mail and shredded paper from offices, because they may contain toxins, which aren't good for the system. Be wary of cardboard, as it cannot be used if it contains wax or plastic, which takes things like cereal boxes, and other boxes designed to hold food items, off the list.

Ideally a worm compost bin should be located in areas where the temperatures are between 40 to 80˚F. Red worms generally prefer temperatures in the 55 to 77 degree range. Another consideration: worms are like people in that they do not like a lot of noise or vibrations. Keep them away from high traffic areas.

What do they eat? First, and foremost, START SLOWLY. It will take time for bacteria to form and your bin can quickly become very smelly if you add too much food, too fast.  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. 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. Worms have a gizzard like chickens so fine grit should be added to help the worms digest food. This gritty material includes cornmeal, coffee grounds and/or finely crushed egg shells (dry the shells and then crush). If you notice odors, cut back on the amount of food or try chopping the food up into smaller pieces.

Harvesting the castings: Once your compost bin is up and running, it requires little maintenance until little or no original bedding is visible and the contents of the bin are reduced in bulk and mainly consist of worm compost, which is brown and “earthy” looking. Once your bin has reached that point, it's time to harvest the worm castings and give your worms new bedding. Castings can be harvested anywhere from two and a half months to every six months, depending on how many worms you have and how much food you're giving them.

There are several harvesting methods. For those with the time and patience or little kids, you dump the bin's contents onto a large plastic sheet and then manually separate the worms from the compost. Children usually love helping out with harvesting worm compost. Remember that your helpers as well as yourself should wear gloves. Once all the worm casings are removed, keep aside some of the compost to mix in with the new bedding and then the cycle starts all over again.

A more common way to harvest is to move everything – worms, castings, bedding, food – to one side of the bin. Pick out partially decomposed materials and push to the other side. Place some food on top of the partially decomposed materials. Replace the lid and leave it alone for a couple weeks. During that time, the worms should migrate over to the new food. Once they've gone to the other side, put on a pair of gloves and harvest the castings. Make sure you don't remove any worms in the process. Then give the worms new bedding mixed in with some residual compost.

Vermicomposting can be easy, fun and rewarding once you get started. For alist of common mistakes, click here.

Worm Facts:

• Baby worms hatch from cocoons smaller than a grain of rice.
• Lacking lungs or other specialized respiratory organs, earthworms breathe through their skin.
• Earthworms have 5 hearts
• Worms have a gizzard to help digest their food
• Worms do not have eyes, but light sensitive cells in their skin

If you have a gardening related question you can contact the UC Master Gardeners at 209-953-6112. More information can be found on our website.