Vermicompost (also called worm compost, vermicast, worm castings, worm humus or worm manure) is the end-product of the breakdown of organic matter by some species of earthworm. Vermicompost is a nutrient-rich, natural fertilizer and soil conditioner. The process of producing vermicompost is called vermicomposting .
The earthworm species (or composting worms) most often used are Brandling Worms (Eisenia foetida) or Red Wigglers (Lumbricus rubellus). These species are only rarely found in soil and are adapted to the special conditions in rotting vegetation, compost and manure piles. Composting worms are available from mail-order suppliers, or from angling shops where they are sold as bait. Small-scale vermicomposting is well suited to turn kitchen waste into high-quality soil, where space is limited.
In addition to worms, a healthy vermicomposting system hosts many other organisms such as insects, mold, and bacteria. Though these all play a role in the composting process, the earthworm is the major catalyst for the composting process.
Vermicomposting bins vary drastically depending on the desired kind of system.
Small-scale systems may use a wide variety of bins. Often, small-scale composters build their own bins. Companies also sell such bins. Commonly, bins are made of old plastic containers, wood, Styrofoam containers, or metal containers.
Some materials are less desirable than others in bin construction. Styrofoam is believed to release toxins into the earthworms' environment. Metal containers often conduct heat too readily, are prone to rusting, and may release heavy metals into compost.
Bins should have holes in the sides to allow air to flow, and a spout that can be opened or closed or holes in the bottom to drain into a collection tray. Plastic bins require more drainage than wooden ones because they are non-absorbent. The design of a small bin usually depends on where an individual wishes to store the bin and how they wish to feed the worms. Most small bins can be grouped into three categories:
- Non-continuous – an undivided container. A layer of bedding materials is placed in the bin, lining 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 is often used because it is small and easy to build. But it is relatively difficult to harvest because all the materials and worms must be emptied out when harvesting.
- Continuous vertical flow – a series of trays stacked vertically. The bottom-most tray is filled first, in a similar fashion to any other bin, 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. Worms finish composting the bottom tray and then migrate to the one above. When a sufficient number of worms have migrated, the bottom tray can be collected and should be relatively free of worms. These bins provide an easier method of harvesting.
- Continuous horizontal flow – a series of trays lined horizontally. This method too relies on the earthworms migrating towards a food source in order to ease the process of harvesting. The bin is usually constructed to be similar to a non-continuous bin but longer horizontally. It 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. In 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.
Most large-scale vermiculture systems do not incorporate a physical bin, because it is impractical. A large system usually uses a windrow, which consists of bedding materials for the earthworms to live in (see bedding below) and acts as a large bin; organic material is added to it. Although the windrow has no physical barriers to prevent worms from escaping, in theory they should not due to an abundance of organic matter for them to feed on. Often windrows are used on a concrete surface to prevent predators from killing the worm population. Another property of large scale windrows is that when fed on one side consistently a wave motion is generated over time.File:Wormbedwave.jpg
When beginning a vermicomposting bin, put moist bedding into the bin, and add as many composting worms as available. In hot climates place the bin in the shade or away from midday direct sun. Quantities of kitchen waste appropriate for the worm population can be added to the bin daily or weekly. At first, feed the worms approximately one-half their body weight in kitchen scraps a day, maximum. That is, if you have 1 kg of worms, feed them about 1/2 kg of kitchen scraps a day. After they have established themselves, you can feed them up to their entire body weight. It is best not to add new food until the old food has been processed by the worms.
Bedding is the living medium for the worms but also a food source. It is material high in carbon and made to mimic dried leaves on the forest floor, the worms' natural habitat. The bedding should be moist (often similar to the consistency of a wrung-out sponge) and loose to enable the earthworms to breathe and to facilitate aerobic decomposition.
A wide variety of bedding materials can be used including newspaper, sawdust, hay, cardboard, burlap coffee sacks, peat moss, pre-composted (aged) manure, and dried leaves.
Most vermicomposters avoid using glossy paper from newspapers and magazines, junk mail and shredded paper from offices, because they may contain toxins which would severely affect the system. Also some cardboard cannot be used if it contains wax or plastic, such as cereal boxes, and other boxes designed to hold food items. Newspapers and phone books printed on regular, non-glossy pages are heavily regulated by the Food and Drug Administration (FDA) and use non-toxic soy and Canola based ink (see Soy ink). Some beddings are easier to use and add food scraps to than others.
- Greens - If too much kitchen waste is added for the worms to process, the waste putrifies. A balance between "green matter" such as kitchen scraps and "brown matter" such as shredded newspaper for bedding must be maintained in order for the worms to do their work. This is often called "carbon to nitrogen ratio", and should be approximately 2:1 (C:N). Covering the kitchen scraps with a layer of "brown matter" has the added benefit of reducing odor and insect problems. Avoid grass clippings or other plant products that have been sprayed with pesticides. In a small bin, this includes banana peels which can kill everything in the bin, if heavily sprayed.
- Meats - Although proteins and fats in meat scraps can be processed by a vermicompost bin, doing so tends to attract scavengers and should be avoided if this is a risk. Worms are unable to break down bone or synthetic material.
Over the long term, care should be taken to maintain optimum moisture levels. In a non-continuous-flow vermicomposting bin, excess liquid can be drained via a tap and used as plant food. A continuous flow bin does not retain excess liquid and requires extra water to be added to keep the bedding moist. It is commonly believed that too many citrus peels in the material to be composted can ca use an intolerable level of acidity, which can be mitigated by adding an occasional handful of calcium oxide (lime). The reason is more likely to be d-limonene, a fragrant chemical present in the rind of the orange, which affects worms.
The pH level should be near neutral or slightly alkaline. Coffee grounds have sometimes been blamed for acidity, but analysis shows they are only mildly acidic with a pH of 6.2. Too much oil or fat can hinder the breathing of the worms, as they breathe through their skin. Worms are said to not like highly spiced foods such as onions, garlic, or heavily salted foods.
Worms and other microorganisms in the composting process require oxygen, so the bin must "breathe". This can be accomplished by regularly removing the composted material, adding holes to a composting bin, or using a continuous-flow bin. If insufficient oxygen is available, the decay becomes anaerobic, like that in swamps and bogs, producing a strong odor offensive to most people.
There are two methods of adding matter to the bin.
- Top feeding — organic matter is placed directly on top of the existing layer of bedding in a bin and then covered with another layer of bedding. This is repeated every time the bin is fed.
- Pocket feeding — a top layer of bedding is maintained and food is buried beneath. The location of the food is changed each time and often the bin is fed in more than one location. As bedding runs low more is added.
Vermicomposters often use a combination of both methods. Sometimes unburied food can attract fruit flies. For this reason, food should be buried at least one inch under the surface of the bedding material.
- Odor, usually due to overabundance of "greens" in the bin, actually too much nitrogen combining with hydrogen to form ammonia. To neutralize the odors, add a fair amount of carbon to the mix. The carbon will absorb the nitrogen and form a compound that is not smelly. Paper and dried leaves are good sources of carbon. But too much carbon slows the decomposition process considerably.
- Pests such as rodents and flies may be attracted by certain materials and odors, especially lots of kitchen waste and especially meat. This problem is largely negated if a sealed bin is used where the pests cannot access the material. Local authorities usually advise to avoid pests by avoiding using materials that attract them, rather than relying on special containers. Ants can become a problem as well. No-see-um netting can be used. Regular mosquito window screen is too large and lets fruit flies and possibly ants in as well.
Red Wiggler worms are not native to North America. They are an invasive species and have become naturalized in most of the globe. Do not dump worm-containing compost in natural areas as they can have the effect of displacing the native worms.
Vermicompost, also known as worm castings and vermicast, is very different from compost produced in compost piles by bacterial decay, and is much richer in many nutrients. Worm compost is usually too rich for use as a seed compost, but is useful as a top layer of soil or an addition to potting composts. Some types of pitted seeds are reportedly easier to germinate when placed in vermicompost for several months.
Vermicompost is beneficial for soil in three ways:
- It improves the physical structure of the soil.
- It improves the biological properties of the soil (enrichment of micro-organisms, addition of plant hormones such as auxins and gibberellic acid, and addition of enzymes, such as phosphates, cellulase, etc.).
- It attracts deep-burrowing earthworms already present in the soil.
Vermicompost can be used to make compost tea, by mixing some vermicompost in water and steeping for a number of hours or days. The resulting liquid is used as a fertilizer.
- This worm's for you Vermicomposting with Nature’s Best Recyclers By Joyce Brau, Summer 1999
- Adventures of Herman the Worm Vermicomposting resources for children from University of Illinois Extension
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