Composting outdoors is wonderful, but it requires space and warmer temperatures. Just because it’s still chilly out or you don’t have much outdoor space doesn’t mean you have to send your kitchen scraps to the landfill. You can easily compost indoors with helpful, wiggly worms.
Using earthworms and microorganisms to convert organic waste into black, earthy-smelling, nutrient-rich humus is known as “vermicomposting.” The whole vermicomposting process is simple, and it results in wonderful fertilizer for your container plants and compost for your garden.
Vermicompost is the compost you get from a worm bin system, which includes both castings and decomposed matter. Castings are the nutrient-rich waste that worms create. This waste is excellent as a top-dressing fertilizer for container and garden plants. Along with worms, a vermicomposting system has naturally occurring microorganisms that help decompose kitchen scraps and, over time, the worms’ organic bedding material.
A variety of containers — including commercially made vermicomposting units, homemade wood or plastic boxes, and galvanized garbage cans — make satisfactory bins. The secret to an odor-free bin is plenty of oxygen. To let air in, the container must have holes in the top, sides, or bottom. To keep flies out, cover the air holes with mesh. The ideal worm bin is usually quite shallow at no more than 12 to 18 inches deep — the more surface area, the better. The size of your bin depends on how much kitchen waste you produce — assume a few pounds per week per person. It’s not at all an exact science, but you can plan on about 1 square foot of surface area for each pound of garbage per week. We estimate that a family of four will produce about 10 pounds of kitchen waste per week, requiring a bin with a surface area of 10 square feet. I recommend a worm-to-daily-garbage ratio of 2-to-1. A family that produces 10 pounds of food waste a week, or about 1.4 pounds a day, will want to start with just under 3 pounds of worms.
Because food preparation is done in the kitchen, the most convenient location for a worm bin might be there, too. An outdoor patio a few steps from the kitchen is an excellent location if it’s not in direct sun. Apartment dwellers often find that balconies are a perfect spot for a worm bin and a small container garden. A well-ventilated garage will work if it never sees freezing temperatures, and a basement is fine if it’s not too inconvenient to deposit food scraps there.
Worm beddings hold moisture and provide a medium in which the worms can work, as well as a place for you to bury garbage. The best choices are some form of cellulose: newspaper strips, shredded computer paper, leaf mold (from the bottom of a decaying leaf pile), coconut fiber, and wood chips — or a combination of any of these. A handful or two of garden soil, powdered limestone, or rock dust (also called rock powder) provides grit to aid worms in breaking down food particles.
Add kitchen scraps as often as is convenient, and add new bedding material occasionally to replace what has decomposed. Each time you look in the bin, check moisture levels and add water accordingly. If you find excess moisture in the bottom, tip the container to pour it off — or use a turkey baster to suck it out.
In about six weeks, you’ll begin to see noticeable changes in the bedding. It will get darker, and you’ll be able to identify individual castings. Even if you add food waste regularly, the bedding volume will slowly decrease. Extensive decomposition takes place as more of the bedding and garbage is converted to earthworm castings. Here are two methods for harvesting your vermicompost after it’s ready.
Method One: If you want to harvest the greatest quantity of high-quality vermicompost (that is almost fully converted to worm castings), the trade-off is sacrificing your worm population. Worms don’t thrive in an almost-all-castings situation. This means you might add garbage during the winter months, and then let your bin sit unattended for three to four months. By summer, you’ll find a bin full of fine, black worm castings with very few worms remaining. In this system, you’ll compost food waste outdoors for the few months that you’re ignoring the worm bin. After those few months, it’s time to harvest the compost and give the worms new bedding in the container.
It’s tricky to harvest all of the compost without throwing out your worms, but it’ll get easier with practice. Spread a large plastic sheet on the ground and dump the entire contents of the worm bin onto it. Begin making pyramid-shaped piles. The worms will try to get away from the light by burrowing into the center of the piles. Begin to handpick worms into a separate container as you gently remove a bit of compost from the top and sides of each pile, a little at a time. Eventually, you’ll have mostly separated the compost from the worms, at which point you can add the worms to a freshly bedded bin.
Method Two: This easier method results in retaining more worms but produces somewhat less usable compost, which must be harvested every couple of months instead of all at once a few times a year. You’ll need to add fresh bedding when the bedding has diminished so much that you can no longer dig a hole in which to bury garbage. Push all of the bin contents to one side, and then add new bedding to the empty side. Bury garbage in the new bedding, and the worms will find their way to it. You can harvest fertilizer from the vermicompost side every couple of months.
Many kinds of worms break down garbage, but for vermicomposting, red worms (Eisenia fetida, or “red wigglers”) are best and can be easily shipped to your home. You can find red worms at these online retailers:
What Can I Compost in a Worm Bin?
• Any vegetable waste (peels, rinds, outer leaves, and chopped ends)
• Plate scrapings and spoiled foods, including vegetables, fruits, grains, and dairy
• Coffee grounds, tea leaves, tea bags, and coffee filters
• Crushed eggshells
• Too much citrus, vinegar, or other acidic items all at once
• Meat or bones (the worms can handle some, but too much will cause unwanted odors and pests)
• Pet feces
Healthy, Happy Worms
Temperature: Red worms convert waste best at temperatures between 59 and 77 degrees Fahrenheit, but they can also plow through garbage in a basement bin with temperatures as low as 50 degrees.
Moisture: Worms need moisture to live. Add water to bedding as necessary to maintain uniform dampness, but avoid standing water.
Acidity: Slightly acidic conditions are best. Though worms can tolerate a wide pH range, too much acidic food introduced all at once can actually kill them.
Ventilation: Air circulation is vital. Worms need oxygen, and aerated compost smells earthy; lack of air can lead to bad odors.
Adapted from Worms Eat My Garbage by Mary Appelhof, published by Worm Woman, Inc. and distributed by Chelsea Green Publishing.