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Wisconsin Natural Resources magazine

Wisconsin Natural Resources magazine

Preparing shredded paper for worm bedding. © Robert Queen

December 1998

Composting with worms

A segment-by-segment approach.

Maureen Mecozzi

Preparing shredded paper for worm bedding. © Robert Queen

The bin | Build your own wooden box | The bedding
The worms | The menu
Composter's Corner: Joan North

To begin vermicomposting, you'll need four things: A container for your worms, a supply of biodegradable bedding, a supply of food waste – and worms, of course. You'll find plenty of options and possibilities for each. You could, for instance, use an old dresser drawer for your bin. Or buy a deluxe, everything-but-the-kitchen-scraps vermicomposting system. Select the components that are easiest for you to obtain and maintain.

The bin

Wooden boxes, metal tubs and plastic basins work well as worm containers, provided they allow for good air circulation – the secret to an odor-free bin. The key criteria to consider in choosing or making a bin are:

  • Depth: The worm container should be shallow, no more than 18 inches deep. Redworms feed near the surface, so there's no need for anything deeper. Bedding will mat down in a deeper bin, developing a smell if it starts to decompose anaerobically.
  • Length and width: To determine the length and width of your bin, it helps to have an idea of how much food waste your household creates in an average week. There are two ways to do this:
  • Calculate: Weigh your kitchen scraps for a couple of weeks during a period when you're not canning fruits and vegetables or doing a lot of entertaining. Determine the average number of pounds produced weekly. To size your worm bin, allow one square foot of surface for each pound of scraps per week. Example: If your household creates an average of four pounds of food waste each week, a 2x2' bin should be adequate.
  • Estimate: Size your bin by allowing about two square feet of surface for each person in your household. For a family of three to six people, try a bin that's 2x3'. Adjust the dimensions based on how often your family eats out, cans or freezes produce, or discards leftovers.
  • Surface area: Can't decide between a round or rectangular bin of equal volume? Choose the one that offers the greatest surface area. Air will circulate better and you'll have more places to bury your waste.
  • Cleanliness: Plastic and metal containers, new or old, should be scrubbed with detergent and rinsed with hot water before use. New wooden boxes should not be made of wood treated with preservatives. Avoid any container formerly used to store chemicals or pesticides.
  • Drainage: Most container designs call for 1/4" drainage holes drilled through the bottom. Make 14-20 holes in a plastic container, 9-12 holes in a wooden container. To provide good air circulation, raise the bin up on bricks or wooden blocks, and place a tray or a sheet of plastic underneath to catch any liquid. If the container provides good air flow by running perforated pipes through the bin, drainage holes may not be needed.
  • Location and temperature: Put your bin in a spot that's convenient for you to access, and where worms won't be subjected to temperature extremes. Worms work best at temperatures ranging from 55-77° F. Basements, heated garages or breezeways are usually good sites.

Build your own wooden box

Use 5/8" exterior grade plywood, with the exterior side facing inside, or scrap lumber. (Don't use treated wood.) Using screws, or nails with a spiral shape, will hold the box together under alternating wet and dry conditions. Any wooden box will last longer if it's allowed to dry thoroughly after harvest.

For a 2'x 2'x 10" box (suitable for two people, or up to four pounds of scraps per week)

  • Sides: 22 3/4" x 10"
  • Ends: 24" x 10"
  • Bottom: 24" x 24"
  • Top: 24" x 24"

For a 2'x 3'x 12" box (suitable for three to six people, or up to six pounds of scraps per week)

  • Sides: 34 3/4" x 12"
  • Ends: 24" x 12"
  • Bottom: 24" x 36"
  • Top: 24" x 36"

Assembly: Nail or screw the ends to the outside edges of the sides. Secure to bottom with five to seven nails or screws per side. Drill nine to 12 quarter-inch drainage holes evenly spaced across the bottom surface. The top is not attached; it just slides on or off.

Options: Nail 2"x2" pieces along the inside bottom edges for support. Attach four small wooden blocks to the bottom corners to raise the box off the ground – or secure four casters to the bottom corners for a box-on-wheels. Use gate hinges to attach the top to the box.

The bedding

Besides giving worms a place to work and rest, bedding helps retain moisture in your box and keeps your scraps under wraps. Use light, fluffy biodegradable materials free from pesticides or chemicals. Try the following beddings in your bin.

Machine-shredded newsprint or computer paper: Recycling centers and pet shops may carry this material, or inquire at offices. Make sure no glossy or colored paper is used.

Hand-shredded newsprint or computer paper: Tear newspaper (without the color comics and glossy advertisements) into strips, the thinner the better. Thick strips mat down, dry out too fast and make it difficult to bury scraps.

Shredded cardboard: A good bedding material that holds moisture well. Check your recycling center for sources.

Leaves: Although leaves are a worm's natural habitat, they're not the best bedding for worm bins. Leaves tend to mat down, may harbor undesirable insects, or contain road salts and chemicals. If you do use leaves, gather them from a low-traffic area.

Enhance your bedding with the following additives and your worms will work double-time:

Peat moss absorbs excess moisture and breaks up heavy bedding. Try one-third to one-half peat moss in your bin.

Sterilized soil or sand contribute nutrients and grit to help worms digest food waste. Toss in a handful or two when preparing fresh bedding.

Crushed eggshells or ground limestone add grit and calcium; periodically sprinkle small amounts in the bin.

The worms

Now comes the fun part – choosing your worms. No garden-variety worms for you, friend. In fact, you'll want to avoid nightcrawlers and other garden worms, as they don't survive well in the confined conditions of a worm bin.

The best worms for vermicomposting are redworms. The redworm (Eisenia foetida or Lumbricus rubellus) goes by a number of names: red wiggler, manure worm, red hybrid, striped worm, fish worm – to list just a few. Whatever it's called, the redworm is the worm capable of reproducing quickly, in confinement, while chomping copious quantities of food waste.

You can buy worms by the pound.

© Robert Queen.
Worms by the pound. © Robert Queen

How many worms should you start with?

Base the calculation on the average amount of food scraps your household produces per day. Use roughly two pounds of worms to one pound of daily scraps.If your household produces a half-pound of scraps daily, a one-pound package of worms should be enough. Or, guesstimate: use one pound of worms for a 2'x2' bin; two pounds of worms for a 2'x3' bin.

If you don't want to start with that many worms (one pound contains about 1,000 worms) get a smaller quantity and reduce the amount of food waste in the bin until the population increases. You won't have to wait long: Breeding worms can lay two or three cocoons per week that will hatch in 21 days, with each cocoon hatching two or three worms that will mature in 60 to 90 days.

Here we must call for calm: There's no need to stand guard at the basement door, broom in hand, to sweep back a worm invasion. These creatures understand the ecological concept of carrying capacity much better than humans do. A worm population eventually stabilizes at levels that can be supported by the food scraps added, and by the availability of room to move and breed.

Worm wisdom

You can buy worms from growers, bait shops, some garden centers, or through the mail. Prices range widely; expect to pay about $12 to $18 per pound (1998 prices). If you're reluctant to actually pay for worms, scrounge around an old leaf or manure pile, where you may find a few hardy redworms upon which to build your vermicomposting empire. Check with your local University of Wisconsin Extension office for names of worm growers who sell redworms by the pound. Bait stores typically sell them by the dozen or in small containers that tend to be more expensive.

The menu

Worms are true gourmands. They will eat just about anything, in quantities that would shame a sumo wrestler. That being said, there are still a few things you should know about what to feed these prodigious consumers:

  • Peels and other vegetable waste: The piece de resistance of a worm's dinner. Potato, carrot and apple peels and parings, orange and grapefruit rinds, onion skins, discarded lettuce and cabbage leaves, stems from grapes and herbs, cores, turnip tops or celery bottoms – worms will devour most any fruit or vegetable waste you can think of, with gusto. Rinse off banana peels before adding them or omit them from your offerings because they readily attract fruit flies. (Some vermicomposters report that their worms do have preferences. Joan North's worms don't care for onions or citrus peels. Cantaloupe is a different story. "A day after I put cantaloupe skins in the worm container, I can actually HEAR them eating," she says. "It sounds like thousands of little creatures smacking their lips.")
  • Coffee grounds and tea leaves: These beverage remnants will enhance the texture of the end product, vermicompost. You can even toss in coffee filters and tea bags – the worms will chew up the porous paper in no time. (You may want to remove the tea bag tag first: colored inks can be toxic to worms, and you can keep the little metal staple out of your compost.)
  • Plate scrapings: The mashed rutabaga your three-year-old son refused to touch (and who can blame him?), unfinished scrambled eggs, Aunt Sally's secret succotash, the spaghetti, salad, veggies, gravies – all of it can go in the bin.
  • Egg shells: Crush with a rolling pin before adding to the bin for smoother compost later.
  • Spoiled food: Unlike children, worms eat what's put in front of them, so you can include moldy cheese, leftovers leftover a little too long, stale bread, cakes and crackers, and other "aged" foods in their diet. If you want to add something that's really rotten, bury small portions deep in the bedding and cover well to discourage fruit flies.
  • Meat and bones: Small amounts of meat scraps and fat are ok. While vermicomposting rarely smells, meat scraps are a likely first offender. Aristotle called worms 'the intestines of the soil.' You may decide to omit them or wait until you have more experience with the process. If you add meat scraps, grind or chop them finely first, and mix with a bit of sawdust to help the worms digest these items, and to prevent foul odors from putrefaction, which occurs when proteins begin to break down. Bones? The worms will pick them clean, but actual decomposition takes a long, long time – you may not like having whole bones or large bone shards in your final compost. If you can grind up the bones first, you'll be able to add calcium to your compost without attracting every dog in the neighborhood to your garden.
  • NOT on the menu, ever: Dog or cat feces, used kitty litter, or non-biodegradable items such as rubber bands, aluminum foil, bottle caps or glass.

Remember, you're in charge of the menu and the portion size. Be mindful of what your worms eat or ignore, and you'll soon know what you can put in the bin and what you should avoid.

Composter's corner: Joan North

After a long day of guiding students and faculty, Joan North, dean of the College of Professional Studies at the University of Wisconsin Stevens Point, goes home to learn from her worms. A search for a way to handle food waste in winter when the compost heap was in hibernation led her to vermiculture.

North started vermicomposting two years ago with half a coffee can of worms from a friend and a purchased plastic worm bin with a base and three stackable layers. Her biggest concern about moving several thousand red wigglers into the basement was breaking the news to her "ultra-neat" husband. "I practiced," she said. "'At last, the perfect pets!' And 'Honey, don't go into the basement because I have your Christmas presents down there.'"

Coir bedding (made from coconut husks) came with her bin, but coconuts being in short supply in central Wisconsin, Joan soon switched to machine-shredded newspaper. She checks her worms about once a week to make sure they have food. In winter, all the scraps from the family of two go to the worms. "In summer, they share half the leftovers with the outdoor compost bins," she says. "But I make sure that the worms get cantaloupe, their favorite."

For her own peace of mind, Joan keeps a lamp with a low-wattage bulb turned on near the bin. "It reassures me that the worms are staying put," she says. Though its unlikely the worms would ever escape, knowing there's a lid on the bin also helps Joan sleep at night.

"Vermicomposting was a lot easier, much cleaner, and less intrusive than I would have thought," she says. "While I have not gotten to know any of [my worms] personally, I do have a warm feeling about their collaboration with me to improve my garden and indoor plants. They do fine if I leave them for an extended vacation, and don't need shots or leave hair on the couch."

What better endorsement could a worm ask for?