What is vermicomposting? Why use worms? Known also as worm compost, vermicast, worm castings, worm humus or worm manure, vermicompost is similar to plain compost, except that it uses worms in addition to microbes and bacteria to turn organic waste into a nutrient-rich fertilizer.
Vermicompost, or vermiculture, most often uses two species of worms: Red Wigglers (Eisenia foetida) or Red Earthworms (Lumbricus rubellus) rarely found in soil and are adapted to the special conditions in rotting vegetation, compost and manure piles.
How does vermicomposting work? It works like this: after procuring a container and setting it up (more on that in a sec), feed your worms the same organic waste you’d toss in a compost pile — which includes just about all of your food waste, save the animal leftovers — and let them have at it.
They chew on it for awhile, and when they’re all done eating, they poop (hey, everybody does it) and there you go: vermicompost.
The benefits of vermicomposting with worms
In addition to increased nutrient levels, worm castings contain millions of microbes which help break down nutrients already present in the soil into plant available forms. As the worms deposit their castings, their mucous is a beneficial component absent from compost produced by hot or cold composting.
The mucous component slows the release of nutrients preventing them from washing away with the first watering. Worm compost is usually too rich for use alone as a seed starter. It is useful as a top dressing and as an addition to potting mixes at a rate of one part castings to 4 parts mix.Your plants will love it.
Using vermicomposting bins
Unlike compost, which can work its magic in a pile in your backyard, vermicompost requires a bit more structure to work, usually in the form of a bin. Bins can be made out just about anything, but they require drainage and air flow to be built in, so things like styrofoam (very insulating, and may release toxins into the worms’ environment) and metal (too conductive of heat and cold) are generally less desirable, and plastic requires more drainage than wood be it can’t absorb moisture. The design of a bin usually depends on where you want to store the bin (in your kitchen, basement, backyard, etc.) and how they wish to feed the worms.
Most small bins can be grouped into three different groups:
Three categories of vermicomposting bins
- Non-continuous bins are undivided containers that start with a layer of bedding materials — shredded paper and the like — that line the bottom. Worms are added and organic matter for composting is added in a layer above the bedding. Another layer is added on top of the organic matter and the worms will start to compost the organic matter and bedding. This type of bin popular because it is small and easy to build, but unfortunately they’re more difficult to harvest because all the materials and worms must be emptied out when harvesting.
- Continuous vertical flow bins use a series of trays stacked on top of one another. The tray on the bottom, using something like chicken wire as the base, is filled first in the manner described above (bedding, worms, organic waste), but is not harvested when it is full. Instead, a thick layer of bedding is added on top and the tray above is used for adding organic material. When the worms finish composting the bottom tray, they head for more food and migrate to the tray above. When enough of the worms have migrated, the bottom tray can be collected with just a few straggling worms left behind (they can then go in the tray above). Because of the separate tray, these bins provide are easier to harvest.
- Continuous horizontal flow bins use a similar structure to the vertical flow, but line up the trays horizontally instead.The bin is usually horizontally longer than the vertical version is tall, and is divided in half, usually by a large gauge screen of chicken wire. One half is used until it becomes full, then the other half is filled with bedding and organic matter (pictured below). Over time, the worms migrate to the side with the food and the compost can be collected. These bins are larger than a non-continuous system but still small enough to be used indoors, with the added bonus of being easier to harvest.
Vermicomposting: How to get started
When beginning a vermicomposting bin, start by adding moist bedding — things like shredded paper, dead leaves and other materials high in carbon (it’s should mimic the worms’ natural habitat, in dried leaves on a forest floor) — into the bin, and add the worms to their new home.
Bedding is the living medium for the worms but also a food source, so it should be moist (something like a wrung-out sponge) and loose to enable the earthworms to breathe and to facilitate aerobic decomposition. Other common bedding materials can be used including newspaper, sawdust, hay, cardboard, burlap coffee sacks and peat moss.
Most vermicomposters avoid using glossy paper from newspapers and magazines, junk mail and shredded paper from offices, because they may contain toxins, which aren’t good for the system. Be wary of cardboard, as it cannot be used if it contains wax or plastic, which takes things like cereal boxes, and other boxes designed to hold food items, off the list.
A few tips: In warm climates, especially in the summer, keep the bin in the shade or away from midday direct sun — just like compost, it should stay moist.
Quantities of kitchen waste added depends on the size of the worm population; at first, feed the worms approximately one-half their body weight in kitchen scraps a day at most. That is, if you have one pound of worms, feed them about 1/2 pound of kitchen scraps each day.
When they become more established, you can feed them closer to their entire body weight, though it’s best to wait to add new food until the old food has been processed by the worms.
Troubleshooting odor and pests in vermiculture is similar to the same procedures used in composting; if the bin starts to stink, it’s probably because there is too much nitrogen (which comes from “greens,” which are things like grass clippings), so add some high-carbon “browns” (things like dead leaves and shredded paper), keeping the ratio the same as in conventional composting, about 30 parts carbon to one part nitrogen (see our piece on compost for more details on this).
Rodents and flies are attracted by certain materials and odors, especially meat. This problem can be avoided by using a sealed bin, since the pests can’t get at it, though simply avoiding animal products, rather than relying on special containers, is probably the easier way to go.