Vermicomposting is one of the best ways for people in small homes or apartments to compost and reduce the amount of waste that ends up in the garbage dump.
So what is vermicomposting? What are worm castings? And how can you easily (and cheaply) set up your own vermicompost bin your home?
Vermicompost, or worm composting, is the product of the decomposition of organic matter by worms, usually a breed called red wigglers.
In other words, you feed organic matter (like shredded paper and vegetable scraps) to your worms, who eat them, digest them, and defecate worm castings that can be then used as compost in your garden.
Worm castings is another word for the end product of vermicomposting. Other terms include worm manure or worm compost. Finished worm castings are dark brown round pellets, looking similar to rich soil.
When worms eat, their organic matter travels down a long digestive tube with several sections. The esophagus adds calcium carbonate. The gizzard adds enzymes to help digest and uses grit like mineral particles to smash the food into small particles. In the small intestine, fluid is added to further digest the food and the worm absorbs the nutrients it needs.
While this is going on, the digestive system controls the moisture and the pH level of the organic matter in a way that encourages microbial growth. Worm castings have 10-20% more microbial activity than other forms of compost and the digestion process suppresses harmful pathogens.
At the worm castings stage, it’s still not nutrients but organic matter broken down from larger pieces into smaller. They’re just so small that we can’t see them through the naked eye and it looks just like dirt. The added microbes (and microbes found in healthy soil) are what break down this organic matter into the nutrients that plants can then absorb.
Instead of vegetable scraps ending up in the garbage dump, where they can’t decay due to anaerobic conditions, you’ll be turning them into beautiful compost.
While most composting methods use fruit and vegetable scraps, you generally need 30 times more carbon than kitchen scraps. With enough worms, vermicompost can compost all your kitchen scraps with less carbon.
Other composting methods, like hot composting, require large amounts of organic material to start. Hot composting needs at least a cubic yard to reach high enough temperatures.
But worm composting can be as big (farm-scale) or as small as you need it to be to fit the amount of kitchen scraps and carbons your household produces.
And unlike bokashi, where you need to bury the fermented organic matter in the soil to finish composting, vermicompost is ready to use.
Vermicompost doesn’t smell, so you can compost in small apartments.
While other outdoor composting methods slow down in the cold winter months, vermicomposting can continue at the same pace if the bin is kept indoors.
Like other forms of compost, vermicompost helps you turn clay or sandy soil into beautiful, aerated loamy soil that holds the right amount of moisture to keep your plants watered. The nutrients will encourage big vegetable yields and blossoms.
Compost also supports healthy beneficial microbes which in turn support your plants. The best soil for gardens contains 5% organic matter.
Because vermicomposting is done at a lower temperature than hot composting, more nitrogen remains in the final compost.
Jim – the gardener will explain the basics of starting your own compost station and the benefits it can bring:
To set up a vermicompost bin in your home, you’ll need 4 things:
- Vermicompost Bin
- Worms (Red Wigglers)
- Food scraps
Vermicompost bins can be made with either plastic (like a Rubbermaid tote) or wood (except pressure-treated lumber due to the toxins remaining in the wood).
Bins come in 3 types:
#1 Single Bin
This is the simplest vermicompost bin, using a single container with air and drainage holes to hold the worms, food scraps, bedding, and worm castings.
The upside to this bin is that it’s really easy and the least expensive to DIY as you only need 1 large plastic bin. The downside is that it’s harder to harvest the worm castings without taking the worms or kitchen scraps too.
#2 Stacked Bins
Instead of a single container, you use 3 or more stacked upon each other.
The bottom container is to contain the moisture (or worm tea) that drains from the upper stacks.
The top containers are where the worms live. Using one layer at a time, you start the worms off with bedding and kitchen scraps.
Once that container is full and the worms have turned most of the organic matter into worm castings, you then add a layer on top, with drainage holes for the worms to go through, with fresh bedding and kitchen scraps.
The worms migrate to the next layer in search of food. You then can easily remove the previous container to harvest the worm castings without the worms.
You can DIY your system or buy one for about $100 – $300.
#3 Continuous Flow-Through
Made out of canvas or plastic, the continuous flow-through is a step up from the single bin while still being a single container.
The difference is that there’s an opening at the bottom to harvest vermicompost. When you continually add new kitchen scraps and bedding to the top, the worms keep working their way up, leaving the worm castings at the bottom.
When you open up the bottom, the worm castings come out but not the worms or kitchen scraps. The worms remain undisturbed.
Building a single compost bin is easy!
- Acquire a bin, whether buying a Rubbermaid bin (not transparent), building a wood box, or reusing items like dresser drawers. (If you do use wood, make sure that the wood that worms come in contact with is NOT pressure-treated or stained, as the wood contains harmful chemicals.)
- Drill ¼” air holes every two inches around the top of the bin and into the lid to provide airflow.
- Drill ⅛” holes every two inches along the bottom of the bin to allow drainage.
- Set the bin inside another container to collect the worm tea or liquid that drains out. This container can be another same-size bin (although you’ll want to make sure it doesn’t cover the air holes) or you can use a shorter container that the bin can comfortably sit inside. You may also want to lift the vermicompost bin a couple of inches off this container rather than letting it sit flat.
To make a stackable bin, repeat this process to create as many upper layers as you want.
Avoid transparent bins! Red wigglers are photosensitive and crawl away from the light into darkness.
A larger surface area is better than a deep container, is it better mimics the red wiggler’s natural habitat.
You will also want a bin that’s the right size for the amount of scraps your household produces.
According to the Canadian Wildlife Federation, a 37.9L or 10-gallon tote should suffice for 1 or 2 people.
For 3 – 4 people, double that. For 5 – 6 people, triple that or use multiple vermicompost bins.
You can keep your vermicompost inside or outside.
Worms prefer the temperature to be between 17C to 22C (or 60F to 70F). While they can tolerate hotter and cooler temperatures, their digestion will slow down if it’s cooler. If temperatures reach below 4C (40F), the vermicompost bin needs to be insulated.
Avoid leaving your bin in direct sun. If you keep it outdoors, place it in the shade.
If you’re keeping your bin indoors, then popular places include under the kitchen sink, in the bathroom, in a garage, or in a basement. Just ensure that wherever it is, it’s kept in the right temperature range, out of direct sun, and has plenty of air. Healthy vermicompost bins don’t smell, so you needn’t worry about odours.
You will probably also need to keep vermicompost bins out of the hands of small, curious children (unless supervised; vermicompost bins are great for getting little ones interested in gardening and nature).
Not all worms are equal. While it’s tempting to dig up earthworms from your garden, earthworms or nightcrawlers are not suited for vermicompost. Nightcrawlers prefer to live deep under the soil, moving up and down to eat, aerating the soil but also mixing up the layers. Great for your garden bed but not for your vermicompost bin.
The best worm for vermicompost is either red wigglers (Eisenia fetida) or red earthworms (Lumbricus rubellus) because they:
- Prefer living in compost or leaves (carbon) rather than in soil.
- Breed prolifically as they’re hermaphroditic.
- Process organic matter quickly.
- Live in the top 6” of soil, which suits vermicompost bins and makes it easier to harvest the worm castings without the worms.
Red wigglers can be obtained either from a vermicompost breeder (Google to see if there’s a local company selling them) or from a pet store, where they’re sold as live food.
A vermicompost company may also sell you appropriate bedding and/or a vermicompost kit to start off right.
Buying local is best. Ordering by mail depends on the weather and how long it’ll take in transport. If you do need to order by mail, so long as some of the worms survive transport, they’ll be able to recover and breed more. Add the worm remains to the vermicompost and they will become part of the worm castings.
Red wigglers eat the equivalent of their body weight every day, and 50% of that is kitchen scraps. The other 50% is bedding. A good rule of thumb is 1lb of worms per 500g of food scraps each day.
So, to figure out how many worms you need, weigh your kitchen scraps for a week to figure out the average amount of scraps you’ll have.
All compost requires carbon (browns), and while you don’t need to strictly monitor the carbon to nitrogen ratios in vermicompost, you do need to add plenty of carbon in the form of bedding. The bedding is where the red wigglers live and half of what they eat.
Bedding options include:
- Shredded paper (avoid glossy coloured paper, and if you use newsprint, make sure it’s printed with vegetable or soy-based dye)
- Shredded cardboard (same caveat as shredded paper)
- Coconut coir
- Chopped-up straw
- Peat moss
- Dried leaves
- Whatever bedding you decide to use, make sure that it’s shredded into smaller pieces to make it easier for worms to eat and digest.
You will also need grit to aid the worms’ digestion such as:
- Coffee grinds
- Garden soil
- Crushed eggshells
Worms don’t have teeth, so grit helps them digest food.
Remember to keep topping up the bedding as it disappears!
Things you CAN feed your worms:
- Fruit peels (except citrus) and melon rinds
- Vegetable scraps (except onions and potatoes)
- Coffee grounds and used tea (if bagged, check that the bag is compostable or remove the tea from the teabag)
- Grain products like bread, unsweetened cereal, plain pasta, and cornmeal
- Carbon, including shredded paper, cardboard, and dried leaves. (See bedding options for more.)
Things you CAN’T feed your worms:
- Meat, fasts, and dairy products (use bokashi instead)
- Animal or human feces
- Citrus fruit and rinds
- Onions and potatoes
Feed your worms 1-3 times a week and watch to make sure that most of the scraps are being consumed. If there’s too many kitchen scraps, the scraps will rot and attract insects.
In between feedings, store your scraps in a countertop compost bin or a container. If you have problems with fruit flies, you may want to freeze the scraps for a few days to kill off any fruit fly eggs. After that, leave the scraps out for a couple of days to start to decay and build up microbes.
You may want to rinse off your kitchen scraps to remove lingering pesticide residue (if not organic) and cut them up into smaller pieces. The smaller the food scraps, the easier they are for the worms to eat and digest, and the faster they break down.
Whichever system you use, setting up your vermicompost bin follows the same steps:
- Fill your main bin with dry bedding material (see bedding material above for options).
- Add filtered water* to the bedding material and mix the contents until it’s the consistency of a damp sponge. (Adding more water or more dry bedding as needed.)
- Drain excess water.
- Add the grit, coffee grounds or soil, with crushed eggshells.
- Introduce the worms to the bin, placing the worms on top of the bedding. They’ll tunnel underneath by themselves.
- Wait 1 or 2 days to feed the first scraps. Bury the scraps a couple of inches under the bedding to prevent fruit flies.
- Continue to feed two or three times a week, burying the food in different places.
- When it gets difficult to bury the food scraps, add more bedding.
* Don’t use water from a water softener as the salt will burn your worms. Best to use filtered water left out so the chlorine evaporates.
Watch along to learn how to create a simple worm bin at home:
You can use one of two methods:
- Dump and Sort. Using a bright light, dump the contents onto a plastic sheet. Separate the contents into two pyramid-shaped piles. Wait 15 minutes for the worms to crawl to the bottom of the piles to avoid the light. Harvest the top part of the pile. Continue until only the worms remain and start a new vermicompost bin.
- Side to Side. Feed the worms on one side of the bin for a few weeks, then feed on the other side. The worms will move to the side with the fresh food and you’ll harvest the worm castings from the other side. Replace the castings with fresh bedding.
Once the current layer starts getting full of worm castings, add the next layer with fresh bedding and fresh food scraps. The worms will migrate to the fresh food source over a couple of weeks. Then the original layer is ready for harvest.
- Place a collection bin under the vermicomposter.
- Open up the opening at the bottom of the composter. If you’re using canvas, you’ll loosen the drawstring. If you’re using a trap drawer, you’ll open that.
- Allow the worm castings to come out into the collection bin.
- Close up when you start getting food scraps and worms.
- Replace the food scraps and worms into the top of the vermicomposter.
- Topdress around your garden plants, trees, and shrubs to add nutrients.
- Sprinkle the worm tea (the liquid that drains out from the vermicomposter) onto your plants.
- Add ¼ cup of worm castings into holes when transplanting perennials and vegetables, or 1 cup when transplanting shrubs or trees.
- Mix 1 part worm castings with 1 part potting soil for seedlings.
Keep worm castings dry but moist by using a plastic container with a few air holes. Allow your worm castings to breathe without being exposed to the elements. Used spinach and greens containers and yogurt containers are great for this.
Vermicomposting is an easy and inexpensive way to compost, whether you’re in a studio apartment, a house with a yard, or even running a farm.
And not only will you have beautiful compost to add to your garden, but you’ll also get to see worms working upfront — and interest your kids in nature.