Ook’s Guide to Vermicomposting

Ook the Library Gorilla and friends did a lot of reading before setting up a worm bin. One thing we learnt is that vermicomposting can be a simple hobby, or a life’s mission. Here at the Dorchester Memorial Public Library, we look on it as a scientific exploration, a work in progress that we are always refining and tinkering with. Here’s what we started with in April 2017, though.

The Worms:
Eisenia fetida / E. foetida is the best species – one common name for them is Red Wigglers. It’s easy to give them the environment they like in a bin. (However, the earthworms you dig up in your garden or find on the road after a rain here in Atlantic Canada prefer to live deep in solitary burrows. They won’t survive in a worm bin, so leave them in the backyard!)

magnified worm
Red Wiggler worm viewed with our Merlin magnifier.

Our Bin

We used a plastic storage tub, 60x40x38 cm – ours was a cheap one, so it won’t be as durable as more expensive one might be. It needs a lid – the worms do not like light (and by ‘do not like’ we mean, it causes them stress and they’ll flee it). You’ll also want a tray under it. The tub should sit up on something as feet to keep it out of the liquid that may drain out of the compost. We just used plastic instant-coffee jar lids to set it on. We ended up buying two tubs and using the second lid as the tray (because that was much cheaper than buying a plastic boot tray), but some people use a second tub as a tray – an inner and an outer bin. If you do that, you still want coffee jar lids or something similar for feet, because you’ll need your ventilation holes in the inner bin to be up above the edge of the outer bin, and you’ll want a gap between your outer and your inner bin, of course.

Toy Gorilla (library mascot) and worm bin.
Ook the Library Gorilla, his puppy puppet, and our worm bin.

The lid and sides need ventilation holes both for oxygen and for humidity-regulation. Worms need air! We drilled small holes (about 2 mm or 1/8”) in the lid and around the sides close to the to the top. Some people make much larger holes for ventilation and tape screen over (on the outside) to keep the worms in. Since the worms don’t like light, small holes should be better if the bin is going to be sitting in a library where there are lights on all day. We didn’t screen the small holes in the side and lid. If the bedding gets too damp or they’re unhappy for some other cause (see below), the worms will scale the sides and find a way out, but we haven’t had a problem with that so far. There are larger holes in the ‘handle’ part of our box as part of its manufacture, which we covered with screen, but we taped it inside and that isn’t working – inside the box it’s too humid for duct tape to stick. However, no worms have escaped so far. We could move the screen over those holes to the outside if need be there but for now we’re not worrying about it.

Some people go without drainage, but you can get condensation building up, or get your bedding too wet, or put too much soggy food in, and that’s bad, so drainage is a good idea. We used the same small drill-bit to make clusters of holes at both ends of the tub. On the outside, we duct-taped sections of fibreglass window screen over areas where we’d drilled holes in the bottom. So far, this has kept the worms in! Any liquid that does drain can be diluted and used on plants – it’s too concentrated (too high in nitrogen, maybe?) to be poured straight onto potted plants, according to some sources. You may not have any liquid drain out. We haven’t so far.

Patches of screen covering small drainage holes.

The basic bedding is shredded newspaper, wetted to be about “as damp as a wrung-out sponge” the sources all say. What we did was cut newspaper into coarse strips with a paper-cutter and then dunk it by handfuls in a pail of water, not leaving it to soak — just in, swish, and out. If you get it too wet, add some dry stuff. You don’t fill the bin – you only want a depth of about 10 cm or so to start with. The bedding should be loose, not packed down. Torn up egg carton is good and quite small children enjoy tearing up and dipping egg carton in water. Yay! A chance to be allowed to destroy things! Apparently printer paper is bad – though nobody seems certain why. Definitely do not use receipt paper since that stuff’s coated with something unpleasant.

It’s best to introduce the worms along with some of the compost they had been living in previously. Some suppliers, such as Worm Composting Canada, ship their worms in a mix that contains compost already, but some come as worms alone, in which case, you might want to put in some compost from your home compost, but you may be getting sowbugs, (harmless) mites, springtails and other invertebrates. This isn’t necessarily bad, but you could end up with fruitflies and things too, which would be a problem in the library, or at least annoying. (More on fruitflies below.) Some sources recommend adding a handful or two of outside earth, for grit and useful microbes. Worms have a gizzard (a bit like birds) and like birds, they need to ingest some grit in order to grind what they eat.

What to feed the worms:
Kitchen waste, such as what you’d put in your outdoor compost, is what you want to feed the worms. Don’t put in anything high in protein – no dairy products, no meat or bones, of course – that sort of material will become very stinky! They also dislike citrus peel and onions, though papery onion skins are fine. Crushed egg shell is recommended in Kalman & Schaub as containing nutrients that worms need. In our library they are mostly living on apple cores and banana peels. Wilted salad, mango skins, fruit that you forgot until far too late, cooked vegetable leftovers – those are all great for your worms. Bread is good, but we’ve found you have to crumble it up fairly finely or you get a big piece of blue mould, which doesn’t seem harmful but you don’t need clouds of blue mould spores in your face when you open the bin. Eventually, the worms will eat the bedding, too, but you don’t want them to have to live entirely on damp newspaper. The popular press is probably not a healthy diet.

How to feed the worms:
Bury the food under the bedding. The worms in your bin won’t be sitting on the surface. It’s recommended that you keep track of where you’ve put the food, to keep the worms moving through the bin as well as to keep track of how much they’re eating, so that you can judge if you need to feed them more or less. If you overfeed, you’ll end up with a tub of rotting food. If that happens, take out some of the stuff that isn’t being eaten. We feed ours once a week, but we don’t have very many. (We started off with just a few dozen worms from a friend.) Some of the resources recommend chopping up the worm-food – this isn’t necessary, but it makes it break down into the rotting soft stuff that the worms can eat much faster. It’s probably a bit slower if they have whole apple cores, etc.

Eventually the bedding will all be black earthy stuff, more or less, and then you need to harvest the worm castings – your compost! We haven’t done this yet at time of writing, but you can find directions on line – you just make cone-shaped heaps on a big plastic sheet, let the worms hide from the light, and keep taking compost off the outside, picking out the worms and their egg-cocoons to go back into the freshly washed bin and the new bedding.

Potential problems:
Overfeeding! Too much food will just rot and get smelly. Also, you don’t want anaerobic composting to happen. (Bacteria of the sort that live in oxygen-starved environments are stinky! Also, they’re bad for the worms.) The bin should be damp, not soggy. It should smell kind of earthy, or like whatever you’ve just put in, apple cores or mushy overripe mango, etc. If it is stinky and unpleasant, there’s a problem that needs dealt with. If you think it’s too wet, add more dry bedding and fluff it all up. You can fluff it up if it’s getting too compacted – newspapers fusing into a lump. (Ours does this because there aren’t enough worms yet.) If it’s too dry, sprinkle it with water, or add some soaked bits of egg carton. If it’s always too wet, consider whether you’re adding too much food, too much really wet food, or whether you should add more ventilation holes.

Fruit flies and fungus gnats. These can live and thrive in worm bins. Fruit fly eggs are on much fruit, but people seem to find that freezing kills the eggs/larvae on your apples, tomatoes, bananas etc, so before you put stuff in the worm bin, freeze it. We have a plastic dish in the little library freezer compartment and put the apple cores in that and feed them (thawed) the next week. A ziplock bag would work too. No problems so far! Another thing people recommend to keep fruit flies in check is a sheet of whole newspaper laid over the bedding. Other things can also live in worm bins, but mostly the things that do are also composters and don’t do any harm.

Worms running away from home. Worms will try to escape if their environment goes bad – too wet, too little food. They will then perish horribly on the desert of the floor. They also don’t always settle in well, apparently, but some of their previous compost helps. We haven’t had any problems this way so far.

Too hot or too cold. Room temperature is a good temperature for Red Wiggler worms. Temperatures too high or too low will kill them. They’re not winter-hardy around here.

A worm cocoon. Several baby worms can hatch from each cocoon.
A worm cocoon. Several baby worms can hatch from each cocoon.

Basic Worm-Care Facts

Bedding: damp shredded paper and a bit of earth
Temperature: 13 to 25 C.
Amount to feed: According to Kalman & Schaub, each worm eats about half its body weight a day. It isn’t necessary to feed them every day – a couple of times a week will do. It’s good to know how many grams of worms you started with, so as to estimate how much kitchen waste you should be feeding them.
What to feed: Fruit leftovers, peels, cores, etc. (frozen for a day or two to reduce the chance of introducing fruit-flies to the compost bin), crushed eggshells, vegetable peelings, cooked vegetable leftovers, leaves, grass, plant trimmings, bread, coffee grounds, teabags, coffee filters, pizza crust, cake, cookies, cereals. More finely chopped up material will break down and be consumed much more quickly.
When to harvest the compost and renew the bedding: Every two to three months (Kalman & Schaub).

A worm in the compost.

Recommended Reading and links to some useful vermicomposting resources

Kalman, Bobbie & Janine Schaub. Squirmy Wormy Composters. New York: Crabtree, 1992. (Unfortunately, this excellent resource for classroom/library vermicomposting is o.p.)

Lewis, Suzanne. Composting for Canada. Edmonton: Lone Pine, 2010. (This is mostly on outdoor composting but has one chapter on vermicomposting.)

Woolnough, Mike. Worms and Wormeries: Composting Your Kitchen Waste … and More. Preston: Good Life Press, 2010.

Worm Composting Canada
One of the best resources we found – they are also a supplier of composting worms and are recommended by the Royal Botanical Gardens in Hamilton as a source of worms for classroom compost projects. Take some time to explore their website.

A Vermicomposting fact sheet from the Oklahoma Agricultural Extension Office:

A guide intended for classroom worm composting:

From the Worm Composting Canada site, a video on other creatures you might find living in your compost. (You’ll want to watch it full-screen in order to be able to read the captions.)