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The Wonders of Waste

Vermicomposting produces homespun organic fertilizer for the gardener, bringing fame to the often-maligned slimy worm.

By Jennifer Cole | July 12, 2024

Vancouver gardener Melanie Semlacher blends her organic kitchen scraps into a slurry and freezes it in ice cube trays. The cubes are not flavour savers for future soups and stews; they’re feed for her worms. “I feed them a cube every couple of days,” she says. As the worms eat the slurry, it passes through their bodies and is excreted as worm manure.

Vermicomposting is popular among home gardeners, especially those with small garden spaces. Living in a Vancouver townhouse, Semlacher’s garden space is limited, but she can still vermicompost by using small Rubbermaid bins she keeps on her balcony. Worms prefer darkness over light, so the first step in creating a vermicomposter is to source a dark plastic or wooden box.

Next, you need the worms. “The best vermicomposting worms are red wigglers,” says Michael Levenston, executive director of the City Farmer Society, because they can consume half their body weight in food at a time and will reproduce quickly, making more compost for the garden. City Farmer Society teaches worm composting at the Vancouver Compost Demonstration Garden on Maple Street in Kitsilano and at schools throughout the city.

Since they are a non-native species in B.C., you can’t find red wigglers by digging up the garden. Garden centres such as Minter Country Gardens in Chilliwack and City Farmer Society are happy to supply the home gardener. Keeping red wigglers contained is a must because they are considered an invasive species. Any vermicomposter must have small air holes at the top just below the lid line and at the bottom so that the worms receive air and their drippings can drain onto a tray placed under the bin. But those holes must be minuscule; otherwise, the wiry red wigglers will escape.

The vermicomposter must stay cool — not too hot or cold — as the wigglers are picky about temperature. An optimal range is between five to 30 C. “I moved my bin indoors when the temperature drops below freezing,” Semlacher says.

To furnish the vermicomposter, fill the bin up to just below the air holes at the top with shredded newspaper, cardboard, straw or dried leaves. Moisten the nesting material with water, but don’t waterlog.

Picky eaters
Now, it’s time for the worms to move in. If a household produces between half to one kilogram of scraps each week, two kilograms of worms are perfect to start. “Feeding the worms too much, though, can cause the environment in the vermicomposter to become unbalanced,” Semlacher says.

They are also finicky eaters and don’t like citrus foods and those in the allium family — garlic, shallots or leeks. These foods are too acidic and will kill the worms. Meat, oils, dairy products, bones, hair and skin products are also not recommended for a vermicomposting bin. Adding coff ee grounds, according to Levenston, will make the worms hyper. “But they like asparagus and avocados,” he says.

When feeding the worms, open the lid of the vermicomposter and bury the food waste just under the surface of the nesting material, keeping it hidden and in darkness. Always make sure the nesting material is moist.

Now that the worms are cozy in their new home, it is just a matter of waiting.

Time to harvest
“It took about three months for the worms to double in number and [produce] enough material to harvest,” Semlacher says. Harvesting was messy. The worms need to be separated from the compost. “It was the most challenging part,” she says.

The best method involves flipping the bin and creating a mountain with the compost. Th e worms don’t like light and will travel to the bottom of the mound, allowing the castings to be harvested from the top of the mountain.

Is all the effort worth it? The nutrient-rich compost is healthier for the soil, and plants become more productive. And for Semlacher, it is just another way she can upcycle her kitchen waste.

“I’ve used the vermicastings as a top dressing for my container plants as well as garden beds,” she says. “It was very thick, had an earthy smell and was dense and dark. From a home gardening perspective, producing vermicastings is a great alternative to purchasing fertilizer.”