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Composting with a worm bin

Tools for living    Natural gardening    Composting guide    Worm composting

Find instructions and materials to build and use your own worm bin for composting kitchen scraps, and how to solve common composting problems.

worm bin cartoon

Worm bins are designed for composting food wastes using red worms (Eisenia Foetida). Vegetable and fruit scraps from the kitchen are added on a regular basis; the worms eat the food waste and turn it into compost.

To set up a worm bin, you'll need:

  • a container that is wide and shallow
  • red worms
  • bedding
  • fruit and vegetable scraps from your kitchen

Fill the container three-quarters full with moistened bedding. Add the worms. Pull aside some of the bedding, bury the food waste and cover it up.

Setting up the worm bin

During a period of two to three months, the worms and microorganisms eat the food waste and bedding and produce a rich compost.

The container and the worms

Build a wooden worm bin (see instructions below), buy a plastic tub with a lid, or use an old trunk or drawer. Wooden containers are absorbent and good insulators. Plastic containers maintain a constant moisture level but may get too wet.

The container should be between 8 and 16 inches deep, with holes drilled in the bottom and sides for aeration and drainage. The bin design in this brochure will accommodate about one pound of red worms (1,000 to 2,000 worms) and process about seven pounds of fruit and vegetable scraps each week. Raise the bin on bricks or wooden blocks for air circulation and to protect from freezing in winter. Place a tray underneath to capture any excess moisture.

Cover the bin to conserve moisture and provide darkness for the worms. Place a sheet of dark plastic on top of the bedding to retard moisture loss and discourage fruit flies.

Worm bins may be located outdoors, or in the basement, shed, garage, balcony or under the kitchen counter. They need to be kept moist, dark and out of hot sun. When temperatures drop below freezing, bins should be moved indoors or be well-insulated.

There are local and mail order suppliers of red worms. Red worms are recommended because they quickly and efficiently process food waste into vermicompost. These worms will probably not survive in your garden. Most suppliers sell red worms by the pound. Availability of worms may fluctuate seasonally. A list of suppliers is available by calling or emailing Metro Recycling Information.

The bedding

Suitable bedding materials include shredded newspaper or cardboard, brown leaves, straw, peat moss and/or sawdust. Mix more than one bedding item in the bin to create an environment with spaces for air and to allow easy movement by the worms. Fill the bin three-quarters full with bedding that has been moistened so it is as wet as a wrung out sponge. Add a handful of dirt to provide necessary grit for the worms' digestion. Cover the bedding with a dark sheet of plastic to maintain a constant moisture level and discourage fruit flies. During the course of several months, the worms will eat the bedding. Add more moistened bedding as necessary to maintain the bin at three-quarters full.

Food waste

Do feed your worms...

  • vegetable scraps
  • coffee grounds and filters
  • tea bags and filters
  • limited amounts of old bread (no butter, mayonnaise)
  • fruit peels or pulp

Do not feed your worms...

  • meat
  • fish
  • dairy products
  • greasy or oily foods
  • pet wastes

To avoid odor or pest problems, do not compost meats, dairy products, oily foods or grains. When adding food waste to the bin, pull aside some of the bedding and bury the food. Bury successive loads in different locations in the bin.

Harvesting your compost and cleaning out the bin

After several months, there should be a marked reduction in the amount of bedding in the bin. Dark, crumbly compost castings will have collected in a layer on the bottom of the bin. It is time to remove some of the finished compost and add new bedding.

The quickest method is to build fresh bedding on one side of the bin and feed the worms on that side only. Wait two weeks until the worms have migrated to that side, then move the bedding from the whole bin to that side. Remove the finished compost from the "worm-free" side of the bin. Use the compost on your house plants, seedlings or for general garden use.

Add new moistened bedding to the empty side of the bin. Next time you add food, put it in the new bedding. The worms will migrate into the new bedding to eat the food.

After several more months, repeat the procedure to remove the finished compost from the other side of the bin.

  • add only enough food that the worms can eat in a few days
  • maintain air spaces in the bedding
  • keep bedding moist but not wet
  • add only the proper food items
  • bury the food waste in the bedding
  • place a dark plastic sheet over the bedding
  • put the bin in a location where a few fruit flies will not bother anyone

Common problems

Odor

To avoid unpleasant odors:

Make sure the worms have the right amount of food. If the worms have too much food to eat, the extra food will rot. Try to stop feeding them for a few days, and break up food chunks to allow worms to eat what is present.

Keep the bin well ventilated. Gently fluff the bin with a gardening fork to break up pockets of aenerobic bacteria (the smelly type). Fluff each day and add loose bedding to the bin. Make certain your air holes are not blocked.

Keep the bin moist, but not soggy. Check to see if the air or drainage holes are blocked. Blocked air or drainage holes can lead to a rise in moisture and a decrease in oxygen, promoting anaerobic bacteria growth. You may be adding too much wet food to the bin with not enough damp bedding. If there is actual standing water in your bin, absorb it with a sponge or paper toweling until the extra water is removed.

Remember to avoid meat, diary and oily foods, which go rancid and cause bad odors.

Fruit flies

To discourage fruit flies:

Add more bedding. This gives bacteria greater surface area and a better chance of increasing the rate of decomposition, preventing fruit flies from having adequate time to reproduce. You can also try adding a cardboard sheet or a layer of plastic on top of the bedding inside the bin. Make sure there's plenty of oxygen if you use the plastic layer.

Make a fruit fly trap. Cut the corner off of a plastic bag and place the cut corner into a cup half filled with vinegar. Rubber band the rest of the bag around the top of the cup, creating a funnel of plastic. Place the trap in a corner of the bin. The flies are attracted to the vinegar, fall in the liquid and drown.

Too hot or too cold

Excessive heat, above 90 degrees or excessive cold, below freezing, can cause the worms to die. If your worm bin is outdoors, insulate it during the heat of summer and the coldest part of winter with straw, brown leaves or an old blanket thrown over the bin. Moving an outdoor bin into the garage or shed will provide protection during hot or cold spells.

Summary

A worm bin is an ecosystem. About eight microorganisms will thrive in your bin with the worms. Together they eat, reproduce and make compost. It is your responsibility to maintain an environment conducive for life. The worms, in turn, will thrive, reproduce and generate an enormous quantity of high-quality compost.

This guide was produced, in part, from information provided by the Capital Region Recycles program, Victoria, B.C.

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