Vermicomposting: Worm Composting Indoors, Part One
(Editor's Note: This article was originally published on September 13, 2007.)
Most gardeners are comfortable with worms, and welcome them into their garden as hardworking partners in soil management. They aerate, they bring organic matter from the surface to deeper levels, and they enhance the microbial environment. These are the earthworms we all know.
But there are other worms that have poor burrowing habits and prefer to live in the littered surface of loose topsoil rich in organic matter. They are the so-called epigeic worms, such as Eisenia fetida (or ‘red wiggler’) and their habitat can easily be duplicated in a closed environment. This is our aim with vermicomposting.
This two-part article will show you how to construct your own indoor worm bin, create the environment, introduce the worms, feed and maintain them, and harvest and use the resulting compost.
A regular RubberMaid or similar brand plastic tote is your starting point. You can use a discreet 10-gallon size, or a larger 25-gallon ‘Roughneck’ storage container. I have one of each.
Your bin will need drainage and ventilation, so drill ½-inch holes in the bottom and lid; if you’re using a large bin, drill holes in the sides as well. Cover the drilled areas with strips of fiberglass window-screening to prevent escapees or uninvited guests. Seal the edges of the screen to the plastic with duct tape. Your bin should sit on a plastic boot tray to catch any drips (leachate).
The bedding for your worms is easily made from newspapers. Tear them into ½ inch strips or run them through a shredder. Wet the shredded paper, squeeze out the excess water and fluff it so you’re left with a loose bedding material that’s uniformly damp. Put a 3-inch layer of bedding into the bin and sprinkle it with about a cup of garden soil. This provides grit for the worms’ gizzards to grind the food they ingest, and introduces an important microbial element to your bin.
It’s best to start out with the right worms: Eisenia fetida is the acknowledged best species for vermicomposting. This ensures that your colony will thrive in the environment you have created, whereas earthworms or fishing-bait worms would not. The photo at left shows my smaller bin with fresh bedding and my newly purchased worms placed on one side, ready to be fed and covered.
Where to get them? If you don’t have friends or connections or a shop that sells them locally, you can search for a supplier online. There are many mail-order companies in North America. They typically charge $25-$30 plus shipping and handling for a pound of worms, which is all you need (they reproduce quickly).
Plop your worms into the bin, add a pound or two of food and cover with another 2 to 3 inches of bedding. Close the bin and try to resist disturbing them. They hate light.
Feeding Your New Friends
All your vegetative waste can go into the bin: fruit and vegetable trimmings, peels and skins; coffee grounds (even the filter) and tea bags; overripe or rotting fruit, or that slimy romaine you forgot about; leftover cooked food (vegetative); even deadheaded blooms and pulled plants from your garden (avoid weed seeds). I’ve found they don’t eat root vegetables like potatoes or carrots (unless cooked or really rotted), or dried things like onion skins. They tolerate an acid environment with a pH of 5.0-5.5.
Don’t add any oil or any animal products (including dairy). Rinsed egg shells are acceptable but they don’t really break down. I don't use them.
Food should be in smallish pieces (under 2 inches). Worms can’t eat cellulose, so tough skins, such as pineapple and cantaloupe (they LOVE cantaloupe flesh) won’t be thoroughly broken down. Some people use a food processor to make a ‘slurry’ of the food, but that’s more work than I’m willing to put into this and the worms don’t really care. The end result will be a little chunky, but we’re making compost here, not a chocolate mousse.
Interestingly, the food we give them is not their main source of nutrients: it’s the bacterial, microbial, fungal growth on the rotting food that they seek. Adding a little garden soil to the bedding helps to establish this microbial environment.
Part Two of this article will cover maintenance of your worm bin, problems and solutions, and harvesting and using your worm compost.