Composting outdoors is wonderful, but it requires space and, in most climates, the warmer temperatures of spring, summer and fall. Just because it’s winter 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.
For help on starting your worm bin read 7 Tips for Setting Up a Worm Bin.
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 worms create. They are excellent as a topdressing 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.
Many kinds of worms break down garbage, but for vermicomposting, red worms (Eisenia fetida, or “red wigglers”) are best. They can be shipped easily. Order them through Worm’s Way or Green Greg’s Garden and Worm Farm. To make your worms happy, consider these conditions.
Temperature: Red worms convert waste best at temperatures between 59 and 77 degrees, 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—no standing water.
Acidity: Slightly acid conditions are best. Though worms can tolerate a wide range of pHs, too much acidic food—such as citrus and vinegar—introduced all at once can kill them.
Ventilation: Air circulation is vital. Worms need oxygen, and aerated compost smells earthy; lack of air can lead to odors.
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 shallow, usually 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 is not at all an exact science, but plan on about 1 square foot of surface area for each pound of garbage per week. For a family of four, we can guess around 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 2:1. The family producing 10 pounds of food waste a week, or about 1.4 pounds a day, will want just under 3 pounds of worms to start.
Because food preparation is done in the kitchen, the most convenient location for a worm bin might be there, too. An outdoor patio off the kitchen is an excellent location if it’s out of direct sun. Apartment dwellers often find balconies 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, wood chips and peat moss—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 suck it out with a turkey baster.
In about six weeks you may begin to see noticeable changes in the bedding. It will get darker and you will be able to identify individual castings. Even if you add food waste regularly, the bedding volume will slowly decrease. As more of the bedding and garbage is converted to earthworm castings, extensive decomposition takes place.
Compost Harvesting Method One: If you want to harvest the most high-quality vermicompost almost fully converted to worm castings, the trade-off is slowly losing your worm population. Worms don’t thrive in an almost-all-castings situation. This means you might add garbage during the winter months then let your bin sit unattended for three to four months. By summer, you will find a bin full of fine, black worm castings, but very few worms remaining. In this system, you’ll compost food waste outdoors for the few months that you are 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 all of 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.
Compost Harvesting Method Two: This easier method results in keeping more worms but turns out somewhat less of the usable compost, harvested once every couple of months instead of all at once a few times a year. When the bedding has diminished to the extent that it is not deep enough to make a hole to bury fresh garbage, it is time to add fresh bedding. Push all bin contents to one side, 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.
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