Worm Composting: Answers to Frequently Asked Questions

Worm House
Image Courtesy of TAW4, FreeDigitalPhotos.net

Worms produce high-quality compost that enriches soil, improves growing conditions, and significantly increases yields.

Worm composting is great for the environment and your garden, and it’s easy to do. Worm compost systems require only a small amount of work to set up, and well-managed systems are odorless and need very little maintenance.

What kind of container do I need for worm composting? Can I make my own worm compost bin?

There are many cool compost bin ideas out there. If you choose to make your own container, drill a dozen holes in the bottom for drainage and place the bin on bricks or find some other way to raise it so that liquid can drain out. Put a tray below the bin to capture this liquid – it can be used as fertilizer. The bin will also need a lid to keep scavengers out. Plastic doesn’t let in oxygen the way wood does, so you’ll also need to drill some holes in the sides for aeration if you use a plastic tub.

Any wood or plastic container around 8 to 12 inches deep will work. The container should have roughly one foot of surface area per pound of household compostable waste generated each week – a  container about 24 by 16 inches wide should be good for a household with two to four people. Containers don’t need to be deep because composting worms live near the surface, but they must be opaque (don’t use a clear plastic container – worms don’t do well in the light).

Upward migrating stacker tray systems work particularly well, are easy to use, and usually come with bedding and other extras. However, they cost approximately $100, so they’re not a low-budget item. I use the Worm Factory 360, which is a great system – easy to use, the worms are thriving, and it doesn’t produce any nasty odours.

Where should I keep my worm composting bin?

Worms do best at temperatures between 40 and 80 degrees Fahrenheit (approximately 5 to 27 degrees Celsius). Many people keep their bins indoors all year round for best results, as worms are most active at the temperatures people prefer.

If kept outdoors, worm systems can be placed in garages or on covered balconies or patios. Wherever you choose to locate your bin, it should be protected from heavy rain and hot sun. If winter temperatures drop much below 40 degrees Fahrenheit/5 Celsius, either move your bin indoors for the winter or find a way to insulate it.

I keep my bin outdoors year-round in a raised, sheltered spot where the temperature tends to be a few degrees warmer than in more exposed areas. The worms reduce their consumption significantly during the colder months, but they don’t die out. However, winters tend to be quite mild in Vancouver, and in areas where temperatures drop below zero for large chunks of time, it’s a good idea to bring the bin into your home or a heated garage for a few months of the year.

A well-managed worm composting system won’t smell bad or attract flies (the first year I had my system, I brought it indoors for the winter and didn’t experience any problems with odours or insects). Your worms will produce compost far more quickly if you have them in a heated space during the winter months.

Where can I get composting worms?

Worm composting is typically done with small red worms (red wigglers). The big whitish worms (dew worms) don’t usually survive in a compost bin.

Composting worms are normally sold in batches of half a pound, one pound, or two pounds. Prices for half a pound of worms are usually around $20 to $25 in Canada. Do a Google search for “worm suppliers” or “compost worms” get a list of suppliers in your area.

How do I set up a new worm composting system? What sort of bedding do the worms need?

Good worm bedding materials include shredded cardboard, newspaper, or dry  leaves; coconut coir; or chopped straw. Dampen the material, add it to the bin, and fluff it up a bit with your hands or turn it with a garden fork so that air can flow through. Throw in a little garden soil and compost to introduce helpful microorganisms (soil contains grit that aids worm digestion as well). Most worm composing experts recommend that worm bedding be as moist as a wrung out sponge.

Worms consume microbes that feed on waste products, so adding the bedding, a bit of soil, and some food waste and then letting the system sit for a week before adding the worms is a good idea. If you want to add your worms right away, add some material to the bin that’s already partly rotted so that there will be some microbes for the worms to feed on.

What foods can I put in my worm composting bin?

Good foods for the worm bin include:

    • Fruit and vegetable trimmings and peelings (or rotten produce), uncooked
    • Shredded newspaper (remove any glossy inserts before adding it to the worm compost)
    • Shredded cardboard or brown paper bags
    • Chopped straw
    • Dry leaves
    • Crushed egg shells
    • Coffee grounds
    • Tea bags
    • Small amounts of starches/grains (pasta, bread, rice, potatoes) once the bin is well established

It’s a good idea to regularly add some dry material (newspaper, cardboard, etc.) with the food waste, as bins with nothing but food waste can become waterlogged, which creates a risk that the worms will drown or the bin will start to smell bad.

Citrus peels are fine in small quantities, but can make the bin too acidic in larger quantities.

Some sites advise against adding starchy or grain products because they can attract rodents to the bin. I occasionally throw in some moldy bread and haven’t had any problems, but my bin is up on the fourth floor. At ground level, worm bins full of starchy or grainy foods are more likely to attract scavengers.

What should I avoid putting in my worm composting bin?

Don’t put any of the following materials in your worm bin:

    • Human or pet waste (due to the risk of spreading parasites and disease-inducing microbes)
    • Meat and dairy products (they take ages to break down, smell terrible, and attract scavengers)
    • Oil or grease
    • Spicy foods (for example, garlic, onions, hot chilies)
    • Salad dressings and sauces
    • Grass clippings in large quantities (they can break down rapidly, releasing ammonia gas, which is toxic to worms, as well as causing the compost to heat up; also, grass doesn’t hold moisture well and may have residues from pesticides and inorganic fertilizers – some pesticide-free grass mixed with brown materials such as dry leaves or shredded newspaper probably won’t do any harm, but avoid adding large quantities)
    • Salty foods (salt dehydrates worms)
    • Chemicals
    • Plastic, foil, glass, and other inorganic materials the worms can’t break down

How often should I feed my worms?

In a well-managed system, a pound of worms can chomp through up to half a pound of food per day. Feed your worms as often as you’d like, but keep in mind that they probably can’t process more than half their body weight per day, and that they’ll slow down their consumption significantly in cooler temperatures. If food starts really piling up in the bin, stop feeding for awhile to let them catch up.

Try to feed a good mix of green (food scraps) and brown (dry leaves, cardboard, newspaper, paper bags, etc.) materials so that the system is neither dry nor waterlogged.

If you have to go out of town for awhile, your worms can be left for up to a month (assuming that your system is in good shape – not waterlogged, smelly, or dry). Just add extra food to the bin before you go.

What do I do if my worms start leaving the bin?

Worms will normally stay inside the compost bin. They only start escaping if conditions are bad (for example, if the bin is out in a hot, sunny spot and overheats or the bedding is too acidic because you’ve added too many citrus peels or other acidic foods). Shift the balance toward milder foods if you suspect that acidity is the problem and be sure to keep the bin in a shady spot if you have it outside.

Sometimes worms will crawl out of a bin when they’re first placed inside because they haven’t accepted it as their home yet. Worms don’t like light, so leaving a light on near the bin during the first night will help to keep them inside for long enough to acclimatize to their new home.

What do I do if the worm composting bin starts to stink?

Worm bins that are properly managed don’t smell unpleasant. If your bin stinks or has become a magnet for flies, there is probably not enough oxygen circulating, and this problem is usually caused by overloading the bin with more food than the worms can eat in a short time. The food sits around and rots, and the bin contents become overly soggy.

If your bin starts to stink, stop adding food waste until the existing food has been broken down, add some dry material such as shredded newspaper or cardboard, and stir the waste to add oxygen to the mix. Drilling more drainage holes in the container can also help.

How do I get rid of bugs in the worm composting bin?

There are various types of bugs you might find in your bin. Mites are common, and usually harmless. I saw them in my worm bin for awhile when I started out, but as the system matured and developed a better balance of materials, they disappeared (I was initially overfeeding with wet produce scraps and not adding enough dry material).

You’re more likely to get mites and other bugs in the bin if you overfeed your worms. If too much food is piling up in the bin or it starts to smell, scale back the food scraps and put in some more dry material such as coir or shredded cardboard so that the environment is less soggy (drill some extra air holes if the system seems waterlogged).

If flies are a problem, bury the food waste under the bedding material and cover the bedding and food scraps with a sheet of plastic. If the problem persists, you can make or purchase fruit fly traps (small containers with vinegar inside and a little hole in the top).

How long will it take my worms to make a finished batch of compost?

The timing is really variable and depends on a number of factors, such as temperature, how finely the materials are chopped up before being placed in the bin, and other factors. Worms will average around two to three months to make a batch of compost in most systems. However, if you chop materials into very small pieces and keep the system indoors during the cold months, you’ll probably get much faster results.

I’ve had very good results with my upward-migrating tray system, sometimes getting an entire tray of compost within a month during spring, summer, and fall (the worms slow down significantly during the winter).

How do I know when my worm compost is done?

Finished compost tends to be black or very dark brown and soft, with a crumbly or muddy texture, depending on the moisture level. It smells earthy – there should be no rotting food smell, and it will have the consistency of soil or mud.

How do I harvest the worm compost?

There are a few ways to separate the worms from the finished compost. You can remove the compost with the worms, spread it out on a sheet of plastic, pluck the worms out (along with any large chunks of unprocessed food), and drop them into fresh new bedding, but this is very time consuming.

An easier option for harvesting is to move the finished or nearly finished compost to one side of the bin and add fresh bedding and food to the other side. The worms will gradually move over to the fresh side and then you can remove the finished compost for use in your garden. It’s a good idea to have a look through the finished compost and transfer any worm cocoons you find to the fresh material (these cocoons, which are shaped like tiny lemons, each contain anywhere from 2 to 20 new worms).

Many people have created their own harvesting systems with tubes or frames and screens to make the process of separating the worms from the compost easier, so this is an option worth exploring if you like to build things.

If you have purchased an upward-migrating tray system, the worms should move up as you start adding food to the higher trays, so you can just remove the bottom trays when they’re finished, dump the compost out, and then add the newly emptied tray to the top of the system. I have a stacker system, so I just wait until the bottom tray of compost is done and most of the worms have migrated upward. Then I pluck out the last few stragglers, dump them into a fresh tray with bedding and food, and add the compost to my garden.

How do I use worm compost in my garden?

Worm compost is great for both in-ground and container gardens. To use it, just mix one part compost with three to four parts soilless potting mix or add a layer of worm compost around the bases of established plants. Some gardeners add worm compost to planting holes to give new transplants a boost.

The liquid that drips from the bottom of the worm bin can be diluted with water and used as a compost tea. Various sources recommend anywhere from a 1:1 dilution to 10:1 water:worm compost liquid. I usually dilute to about 1:1 or 2:1 before adding it to my plants.

More Gardening Articles / Composting FAQ

References:

    • Christie, B. (2014). “Red Worm Composting.”
    • City Farmer, Canada’s Office of Urban Agriculture. (2014, April 2). “Composting with Red Wiggler Worms.”
    • Regional District of Nanaimo. (2015). “Worm Composting.”
    • Rodale. (2015). “Vermicomposting.” Organic Gardening.

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