In the last newsletter I discussed a common form of composting, using a compost pile. This quarter I will discuss the less common method of worm composting.

Worm compost is made in a container filled with moistened bedding and red worms. Add food waste and with assistance from micro-organisms, the worms will convert bedding and food waste into compost. Worm composting can be done year-round, indoors in schools, offices and homes. It is a natural method for recycling nutrients in food waste without odor. The resulting compost is a good soil conditioner for house plants, gardens and patio containers.

How You Do It

Buy or build a box with holes in the bottom. Fill the box with moistened bedding. Add the red worms. Pull aside some of the bedding, bury the food waste and cover it up with the bedding. Add one cup of soil or sand to provide grit for worms' digestive process.

What You Need

  1. a container (made of wood or plastic)
  2. worms (500-2,000 red worms)
  3. bedding (shredded newspaper, corrugated cardboard and/or leaves)
  4. food waste (fruit and vegetable waste)

1. The Container
Photo of compost binsBuy or build a container or use an old dresser drawer, trunk or barrel. Wood containers are absorbent and good insulators for worms. Plastic containers do work but compost tends to get quite wet.

The container should be between 8-12 inches deep and provide one square foot of surface area for every pound of food waste per week (e.g., 6 lbs of waste requires a bin 2 feet by 3 feet or 2 bins 1 foot by 3 feet).

Depending on the container's size, drill 8 to 12 holes (3/16- 1/4 ") in the bottom for aeration and drainage. A plastic bin may need more drainage - if contents get too wet, drill more holes. Raise the bin on bricks or wooden blocks for air circulation. Place a tray underneath to capture excess liquid, which can be used as liquid plant fertilizer.

Worms like a moist, dark environment. Their bodies are 75 to 90 per cent water and worms' body surfaces must be moist for them to breathe. Cover the bin to conserve moisture and provide darkness. Indoors, place a sheet of dark plastic or burlap sacking on top of the bedding. Outdoors, use a solid lid to keep out unwanted scavengers and rain.

Worm bins can be located in the basement, shed, garage, balcony, or kitchen counter. They need to be kept out of the hot sun, heavy rain, and cold. When temperatures drop below 40 degrees, bins should be indoors, heated or well insulated. The container can be heated with an electric heating cable placed in the bottom third of the container. To insulate, surround the container with rigid Styrofoam.

Red worms tolerate a wide range of temperatures, however, the ideal temperature is between 55 – 77 degrees F. Bedding with a temperature above 84 degrees F. is harmful, sometimes fatal, to red worm populations. Measure the temperature inside the box, because the temperature in the moist bedding is usually lower than the outside air.

2. The Worms
Photo of worms in compostRed worms are best suited to worm composting. They are often found in aged manure, compost heaps, and piles of leaves. They are also known as red wiggler, brandling, and manure worms. Their official names are Eisenia foetida and Lumbricus rubellus. Red worms are best suited for composting because they thrive on organic material, such as food waste. Dew-worms, on the other hand, are better suited to life in the soil and shouldn't be used in a worm bin.

You can get your worms from a compost bin, purchase them, or find a horse stable or farmer with an aged manure pile.

For one pound per day of food waste, you'll need two pounds of worms (roughly 2,000). If you are unable to get this many worms at the start, reduce the amount of food waste until the population increases. And the population will increase. Redworms mature sexually in 60-90 days and can then produce cocoons which take 21 days to hatch baby worms. Once they start breeding they can deposit two to three cocoons per week with two baby worms in each cocoon. The limits on their reproduction include availability of food and room to move and breed. So worm populations don't usually exceed the size of the container.

3. The Bedding
Provide damp bedding. Suitable bedding material includes shredded newspaper and cardboard, shredded fall leaves, chopped-up straw and other dead plants, seaweed, sawdust, dried grass clippings, aged manure and peat moss. Peat moss is quite acidic and should be well soaked and combined with other bedding material. Vary the bedding in the bin to provide more nutrients for the worms and to create a richer compost. Two handfuls of sand or soil will provide the necessary grit for worms' digestion of food.

Fill the bin with a mixture of damp bedding so the overall moisture level is like a "wrung-out sponge." Lift the bedding gently to create air spaces. This maintains aerobic activity, helps control odors, and gives the worms freer movement.

4. The Food Waste
Your worms will eat food scraps such as fruit and vegetable peels, pulverized egg shells, tea bags and coffee grounds. To avoid potential rodent problems do not compost meats, dairy products, oily foods, or grains. No glass, plastic or tin foil.

Pull aside the bedding, bury the food waste deep and then cover it up with the bedding again. Divide the bin into three or four imaginary sections (larger bin, more sections) and bury successive loads in different locations in the bin. Keeping a chart of burial sites can be helpful. Weekly food waste will help determine the size of bin and number of worms you'll need. Collect food waste in a container and weigh it. Do this for two weeks to get an estimate of average food waste. Your bin should provide one square foot of surface area for every pound of food waste per week, and you will need two pounds of worms for every pound of food waste per day.

5. Do I need a worm sitter?
If you’re going on a vacation, you could feed the worms a little extra just before you leave. This is the best part of having worms as pets! Feed them and leave them undisturbed. This way, you can go away for weeks. If you leave for longer than 3 weeks, it might be good to have a worm loving friend come and feed them once.

Harvesting Your Compost

After six weeks, the bedding will be noticeably darker with worm castings. After two and a half months have passed, there will still be some of the original bedding visible in the bin plus brown and earthy-looking worm castings. Although food waste is being added regularly, the bedding volume will gradually decrease. As more bedding is converted into castings the worms will begin to suffer. It is time to decide whether you want to do "some fuss" or "more fuss" worm composting.

"Some Fuss" Harvesting
Some fuss worm composting involves moving the finished compost over to one side of the bin, placing new bedding in the space created, and placing food waste in the new bedding. The worms will gradually move over to the fresh bedding and food waste, and the finished compost can be harvested. Fill the space created with new damp bedding.

"More Fuss" Maintenance
If you want to use all of the compost at once, dump the bin's entire contents onto a large plastic sheet and make piles of material. Use sunshine or a hundred watt light bulb to drive the worms to the bottom of the piles. Worms don't like bright light because the single cells on the epidermis (skin) react to light. Scoop off the tops of each pile until all you have left is the worms. Most children love to help! Watch out for the tiny, lemon-shaped worm cocoons that contain the baby worms. Mix a little of the finished compost in with the new bedding of the next bin. 

Common Problems

Unpleasant Odors
Unpleasant odors may waft from your bin when it is overloaded with food waste. If this occurs, gently stir up the contents to allow more air in. Stop adding food waste until the worms and micro-organisms have broken down what food is already in the bin. Check the drainage holes to make sure they are not blocked and drill more holes if needed. If the moisture level seems right, the bedding may be too acidic from citrus peels and other acidic foods. Adjust by adding a little dolomite lime and cutting down on acidic wastes.

Fruit Flies
Fruit flies aren't harmful, but they are a nuisance, and a very common problem with worm bins. Discourage fruit flies by always burying the food wastes and not overloading the bin. Keep a plastic sheet, piece of old carpet or a lid on the compost's surface in the bin. Mary Appelhof, author of Worms Eat My Garbage, acknowledges that she hasn't found the perfect solution to fruit flies. Adding a spider or two helps reduce fruit flies. If flies persist, move the bin to a location where flies will not be bothersome.

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