Oregon State University Extension Service Master Gardener Larry Steele touts the rich nutrition of red-worm manure, also known as castings.
Early in his training, Larry learned the most important lesson in vermicomposting: Don’t use the big worms already wiggling around in the soil. These big night crawlers won’t hang around.
Instead, keep your worm farm working with red worms, found where fish bait is sold and online from outfits that supply vermicomposting equipment.
“If you build a comfortable place for them to live and keep feeding them, they’ll never go away,” Larry says.
Making a comfortable place for the worms is an easy proposition. Make a box by attaching sides and bottom, but leave the top board loose so you can open and close the bin. Don’t forget to drill holes in the sides of the box to give the inhabitants air.
The size of the box depends on the amount of food waste you will add each week. A good rule of thumb is a square foot of box per pound of waste a week. A 2-by-4-foot box with a 12- to 16-inch depth is a good place to start.
Wooden boxes can be set on bricks with a tray underneath to catch the liquid from the vermicomposting process, but it hasn’t been necessary in Larry’s experience.
Newsprint is a cheap and easy option for bedding but only use the black-and-white sections. Tear it into long strips, soak it in water and squeeze until it’s about as moist as a damp sponge. Fluff it up and fill the bottom quarter of the box.
Add worms and cover them with a layer two to three times as thick as the bottom layer. Lay down more bedding when it is reduced by half—about every month or two, depending on the size of the bin and how much food is provided.
Larry says worms have a marvelous capacity to reproduce.
“Eight mature worms can result in 1,500 offspring in six months,” he says.
To feed the worms, pull back a bit of bedding, put in some kitchen or vegetable garden waste and cover it. Worms are top feeders, so they naturally will come to the uppermost layers to eat. As they digest the food, it passes through and comes out as castings—worm manure.
Feed the worms vegetable and fruit scraps, banana peels, coffee grounds and filters, tea bags, crushed eggshells and corncobs. Don’t add meat, fish, bones, oils and dairy products. Be conservative with citrus peels, onions and garlic. Letting scraps sit in a bucket outside to rot a little isn’t a bad idea. Worms go through softer things quicker.
The best location for a worm bin is a garage or shed, but they can be kept outside year-round if filled with enough bedding for insulation. Watch the moisture level, too. In summer, you may need to sprinkle the bin with water to keep it damp enough.
As the castings build up in the bottom of the bin, push aside the bedding and scoop out a double handful of finished product. Take as few worms as possible to keep your worm farm populated.
Put the castings on a table in the sun for about 10 minutes. Since the worms don’t like sunlight, they will retire to the inside of the mound. Gather the worms and return them to the bin.
The castings can be added to regular compost—about 25%—and used to build up beds, or spread them around plants and dig in slightly. Sprinkle castings on potted plants and over garden beds. Other uses include adding to the bottom of planting holes and mixing with potting soil at a concentration of about 20%.
For more information, check out the extension’s publication on composting with worms: https://bit.ly/3aCWnv2.