CORVALLIS, Ore. — Gardeners have long praised compost as “black gold,” and many consider worm castings the “black diamonds” of soil health.
“I started with regular compost,” said Larry Steele, an Oregon State University Extension Service Master Gardener. “But then I took a session in Master Gardener training and the instructor talked about how good worm castings are and how easy it is to make.”
Don’t use big night crawlers from the garden — they won’t stay in a bin. Choose red worms, also called red wigglers or tiger worms. Build or buy a bin, feed kitchen scraps and the worms will produce castings that add nutrients and improve soil structure.
“If you build a comfortable place for them to live and keep feeding them, they’ll never go away,” said Steele, who keeps bins at home and at the Linn County Master Gardener Demonstration Garden in Albany.
Wooden bin
- Make a box from six pieces of plywood.
- Leave the top board loose for access, or add hinges.
- Drill ventilation holes in the sides for air.
- Size to your scraps: plan about 1 square foot of surface area per pound of weekly food waste.
- A 2-by-4-foot box, 12 to 16 inches deep, is a good start.
Plastic bin
- Stack two bins with spacers between them.
- Drill holes in the bottom of the top bin so liquid drains into the lower bin.
- Dilute collected liquid with water and apply around plants.
Wooden boxes can sit on bricks with a tray underneath, though Steele rarely finds that necessary.
“Most of the excess moisture gets absorbed into the wood or just doesn’t materialize as condensation because the wood is a better insulator and warmer surface,” he said. “More moisture escapes because wood breathes and plastic does not.”
Set up bedding
- Use only black-and-white newsprint.
- Tear into long strips, soak and squeeze until as moist as a damp sponge.
- Fluff and fill the bottom quarter of the bin.
- Add worms and cover with a layer two to three times thicker.
- Add fresh bedding whenever it is reduced by half.
How many worms to start
About 1,000 red worms suit a 2-by-4-foot bin, though even a quarter of that works.
“They have a marvelous capacity to reproduce,” Steele said. “Eight mature worms can result in 1,500 offspring in six months.” The bin size and available food keep populations in check.
Buy red worms at bait shops or from vermicomposting suppliers, or get a starter handful from a friend’s bin. Confirm they’re red wigglers, not night crawlers.
What to feed (and what to skip)
How to feed
- Worms are top feeders. Bury scraps lightly under the top bedding, then cover.
- Let scraps soften for a day or two to speed things up.
Feed these
- Vegetable and fruit scraps
- Banana peels
- Coffee grounds and paper filters
- Tea bags
- Crushed eggshells
- Corn cobs
Avoid these (or go easy)
- Meat, fish and bones
- Oils and dairy products
- Large amounts of citrus peels
- Large amounts of onions and garlic
“They don’t have what we think of as teeth, so they work into the softer stuff first,” Steele said. “Take a corn cob. The first thing they consume are the bits of kernel. When that is done, they begin to eat into the core, which is softer than the outside of the cob. Break it in two and there may be 50 worms inside. Eventually, it will disappear.”
Where to place the bin
A garage or shed is ideal. Bins can stay outside year-round if you add enough bedding for insulation. Monitor moisture; in summer you may need to sprinkle the bedding to keep it damp.
Harvest castings
As castings build at the bottom, push aside bedding and scoop out double handfuls of finished material. Try to take as few worms as possible. To separate them, mound castings on a table in sunlight for about 10 minutes; worms will move inward away from the light and can be returned to the bin. If that’s too tedious, you can skip this step but you’ll lose many worms.
Use castings in the garden
- Mix into finished compost at about 25% to build beds.
- Side-dress plants and lightly work into the soil surface.
- Sprinkle a thin layer on potted plants and over garden beds.
- Add a small amount to planting holes.
- Blend with potting soil at about 20%.
Previously titled Red worms eat their way through kitchen waste to produce rich soil amendment
