Composting with Worms

Are you looking for an alternative to trudging through the snow to the compost bin this winter? Then vermicomposting is for you!


Vermicomposting is the process of using worms and microorganisms to turn kitchen waste into a black, earthy-smelling, nutrient-rich soil conditioner. Vermicomposting returns badly needed organic matter to your soil while cutting down on garbage going into your landfill.


Vermicomposting can be done indoors or out, allowing for year-round composting. It is ideal for anyone who may not have regular access to an outdoor composter, such as apartment dwellers.


Vermicompost is made in a bin filled with moistened bedding and Red worms. Food waste is added to the bin for a period of time, and the worms and microorganisms eventually convert the contents of the bin into a compost called “castings.”


The Red worm

The best type of worm to use for vermicomposting is the Red worm, Eisenia foetida. Red worms are incredible garbage eaters that eat and expel their own weight everyday.


Red worms can be obtained from vermicomposting suppliers, bait shops, or friends and neighbours already actively vermicomposting.


Your bin

Plastic storage containers with tight-fitting lids make good worm bins. Another option is to build a bin out of wood. To provide the necessary darkness for your worms, make sure your bin is opaque.


The size of your bin will depend on the amount of food waste generated each week and the number of people generating the waste. In general, provide one square foot of surface area for every pound of food waste generated each week. See the chart below for guideline dimensions.


Number of People Quantity of Worms Bin Size (h x l x w)
1 or 2 1 lb. 1.5’ x 2’ x 1’
2 or 3 2 lbs. 2’ x 2’ x 1’
4 to 6 3 to 4 lbs. 2’ x 3.5’ x 1’


Drill 8 to 10 holes in the bottom of your bin for drainage. Duct tape some fine screening over the holes to stop worms and bedding from falling through. Keep your bin raised with a tray underneath to catch excess liquid that can be used as a plant fertilizer.


Your bin needs a lid to keep in moisture and provide darkness for your worms. Drill several small holes in the lid for ventilation.



Vermicomposting bins can be used indoors all year round and outdoors during the milder months. If you place your bin outdoors, keep it out of the hot sun and heavy rains.


If the temperature drops below 4˚C, move you bin indoors or insulate it against the cold.



Red worms can survive in many types of bedding material. The bedding material you choose must be able to retain both moisture and air while providing a place for your worms to live. Your worms will eat their bedding, turning it into castings.


Common bedding materials include: shredded newspaper, straw, peat moss, shredded cardboard, grass clippings, dried leaves, or a mixture of these materials. Initially, the bedding should fill two thirds of your bin.


It is very important to keep the bedding as moist as a wrung-out sponge. If the bedding begins to dry out, use a fine mist to dampen the bedding again.


When putting in new bedding, fluff it up to create air spaces to help control odours and allow free movement for the worms. Add a couple of handfuls of sand or soil to provide the grit needed by the worms to digest their food.


To add worms to your new bin, simply scatter them on top of the bedding and watch them burrow in to get away from the light.


Feeding your worms

Red worms will eat almost any type of food wastes. Feed them fruit and vegetable scraps, coffee grinds, tea bags, and finely crushed egg shells.


To reduce odours and pest problems, avoid feeding your worms starches, meats and fats.


With a new bin, start slowly until your worms build up their population and can handle larger amounts of food.


Feed your worms once or twice a week by burying your food scraps at least one inch below the surface of the bedding. To speed up the composting process, chop up your food scraps into small pieces. Place the food in a different section of the bin each week.



After about three months, you will start to notice that your worms have converted food wastes and bedding into a mass of rich, dark castings. When the volume of their bedding has decreased and you can identify individual castings, it is time to harvest the compost.


To harvest, take the lid off of your bin and expose the contents to bright light. This will cause your worms to work their way towards the bottom of the bin and allow you to remove the castings a layer at a time.


Most of the worms will be left in a shallow layer of castings at the bottom of the bin. It is time to add new bedding and start all over again.


Using your compost

Compared to ordinary soil, castings have five times more nitrogen, seven times more phosphorus, and eleven times more potassium. The castings you harvest from your bin will provide nutrients for your plants and will help the soil retain moisture.


This compost can be mixed with potting soil and used for houseplants, as mulch for potted plants, or sprinkled on your lawn as a conditioner. In the garden, simply work the compost into the ground around the base of each plant.


For more information on starting and maintaining a vermicompost system, refer to Mary Appelhof’s book “Worms Eat My Garbage” (Flower Press, 1982).


 Past articles are available in this blog under the Watershed Notes Articles category or under Past Articles in the Resources section.