Vermicomposting (indoor method)

courtesy of the Saskatchewan Waste Reduction Council

Vermicomposting is a method of composting indoors using red wriggler worms (Eisenia foetida) in a special aerated bin.

The worms eat plant material placed in the bin which they convert into nutrient-rich compost in the castings they excrete. Beneficial microorganisms in the bin continue to break down and improve the castings. Earthworm castings (vermicompost) are rich in nitrogen, phosphorus, potassium and other nutrients, as well as beneficial bacteria. The nutrients in castings are in a form that is easily taken up by plants. As a soil amendment, worm castings add nutrients, improve soil texture and help to retain moisture.

For a quick overview of vermicomposting see the SWRC's Vermicomposting in 60 seconds video.

Vermicomposting uses red wiggler earthworms to turn food scraps into worm castings. The worms live in an enclosed bin with bedding made of newspaper or cardboard.

To build a worm bin

  • If you are using a plastic tub as your bin, cut holes into the lid and sides near the top to improve airflow. This is  not necessary with commercial vermicompost bins.
  • Add 2-3" of damp, shredded cardboard or newspaper into the base of your tub or bin. You will need to add more on top every couple weeks as the old bedding breaks down.
  • Acquire a starting population of red wiggler earthworms. If you already know someone that vermicomposts, they should have enough worms to give some away every few months. If you do not already know someone, check the SWRC's list of vermicompost suppliers in Saskatchewan. Add your worms to the bin.
  • Add food waste (vegetable and fruit scraps, coffee and tea waste, grain-based products, and egg shells) to the bin. Make sure each addition is covered with at least an inch of the bedding to prevent fruit flies from gathering.
  • If you notice condensation on the underside of the lid, or an unpleasant odour developing in the bin, add some dry bedding and leave the lid off to let it dry out a bit.
  • To control fruit flies (light coloured tiny flies), keep 1-2 apple cider vinegar traps near the bin. (Pour 2-3 cm of apple cider vinegar in a glass and add a drop of dishsoap. This will drown flies. Dump and refresh the trap every week or so.)
  • To control fungus gnats (dark coloured tiny flies), remove the top inches of bedding and dispose of them. Add new bedding. This should quickly reduce fly numbers.
  • If all else fails when controlling flies, add some food for the worms and then spread a 3 cm layer of dry peat moss overtop of the whole bin. Don’t disturb this layer for about 2 weeks.

Depending on how many worms are living in the bin and how heavily they are fed, you should be able to harvest some castings every few months. In a plastic tub, this can be done one of two ways. You can add food waste to only one side of the bin for 3-4 weeks so the worms migrate to that side, and then remove the other half's castings. You can also dump the contents of the tub onto a tarp under a bright light and spread them out. After half an hour, the worms will have hidden at the bottom of the contents and the top can be skimmed off. This can be repeated 2-3 times. Commercial bins have their own specific methods of harvesting.

For more detailed information, download the SWRC's Vermicompost Fact Sheet.

What composting style does it fit?

Vermicomposting requires some knowledge but little work to maintain, so it works well for both hands-off and hands-on composters.

What space does it need?

During most of the year, vermicompost will need an indoor space. Vermicomposters also have the option of putting their system outside during temperate weather (15-30°C).

How does it work?

Vermicompost uses on red wiggler earthworms. The red wigglers eat food waste once it begins to soften from decay, and produce worm castings (droppings). Worm castings are higher in nutrients than regular compost and can be a powerful fertilizer in gardens or used as 10% of a potting mix.

Red wigglers are not the same species of earthworm that live outdoors in Saskatchewan. Saskatchewan's earthworms require 2-3 feet of room to burrow up and down in the soil, and do not thrive in an enclosed bin. Red wiggler earthworms come from warmer coastal climates, where they typically live outdoors in manure and rubbish piles. Red wigglers worms cannot survive a hard frost and will die if left outside in Saskatchewan's winter climate.

Can you use it all year?

Vermicompost is an indoor system and can be used all year. 

Testing it out


Q: Can any type of worm be used for a worm bin?

A: Red wrigglers (Eisenia foetida) are a species of worm that do not burrow into soil which makes them well-suited to vermicomposting. Their native habitat is areas rich in organic matter, such as the upper topsoil layer; or in forest areas under piles of leaves or decaying logs.

Q: Where can I buy red wrigglers?

A: If you live in Saskatchewan see the supplier list available on the Saskatchewan Waste Reduction Council link above. These worms can sometimes be found at fishing supply stores. If you live outside of Saskatchewan, type "red wriggler worm supplier" in your search browser to find a local source.

Q: Will red wriggler worms survive the winter in my outdoor compost bin?

A: Red wrigglers survive winter in warmer climates such as southern Ontario or BC. They are unlikely to survive winter on the cold Canadian prairies and far north because they do not burrow deeply into soil. 

Q: How much vermicompost can I use on my plants?

A: Nutrient levels vary from batch to batch, but a little goes a long way to benefit soil and plants. For indoor gardening, mix 2 - 3 cups of vermicompost into a 40 L bag of seed starting soil or potting soil. Use this for starting seeds or planting up small containers. Otherwise, scatter a tablespoon of vermicompost on top of soil in potted indoor or outdoor plants. Since vermicompost is slow-acting, it is difficult to over apply. 

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