Vermicompost

Rotary screen harvested vermicompost, composed of worm castings

Vermicompost is the product or process of composting using various worms, usually red wigglers, white worms, and earthworms to create a heterogeneous mixture of decomposing vegetable or food waste, bedding materials, and vermicast. Vermicast, also called worm castings, worm humus or worm manure, is the end-product of the breakdown of organic matter by an earthworm.^[1] These castings have been shown to contain reduced levels of contaminants and a higher saturation of nutrients than do organic materials before vermicomposting. ^[2]

Containing water-soluble nutrients, vermicompost is an excellent, nutrient-rich organic fertilizer and soil conditioner.^[3] This process of producing vermicompost is called vermicomposting.

Suitable species

The earthworm species (or composting worms) most often used are Red Wigglers (Eisenia foetida or Eisenia andrei), but Lumbricus rubellus (a.k.a. red earthworm or dilong (China)) are another breed of worm that can be used but adapt less well to the shallow compost bin than Eisenia. European nightcrawlers (Eisenia hortensis) also may be used. Users refer to European nightcrawlers by a variety of other names, including dendrobaenas, dendras, and Belgian nightcrawlers. Lumbricus terrestris (a.k.a. nightcrawlers (US) or common earthworm (UK)) are not recommended as they burrow deeper than most compost bins can accommodate.^[4].

Blueworms (Perionyx excavatus) may be used in the tropics^[5]. However, P. excavatus worms are not suitable for worm compost bins in most of the contiguous United States.^{[citation needed]}

These species commonly are found in organic-rich soils throughout Europe and North America and live in rotting vegetation, compost, and manure piles. They may be an invasive species in some areas^[1][6]. As they are shallow-dwelling and feed on decomposing plant matter in the soil, they adapt easily to living on food or plant waste in the confines of a worm bin.

Composting worms are available to order online, from nursery mail-order suppliers or angling (fishing) shops where they are sold as bait. They can also be collected from compost and manure piles. These species are not the same worms that are found in ordinary soil or on pavement when the soil is flooded by water.

Large scale

Large-scale vermicomposting is practiced in Canada, Italy, Japan,malaysia, the Philippines, and the United States ^[7][8]. The vermicompost may be used for farming, landscaping, to create compost tea, or for sale. Some of these operations produce worms for bait and/or home vermicomposting.

There are two main methods of large-scale vermiculture. Some systems use a windrow, which consists of bedding materials for the earthworms to live in 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 gaining access to the worm population.

Movement of castings through a worm bed.

The second type of large-scale vermicomposting system is the raised bed or flow-through system. Here the worms are fed an inch of "worm chow" across the top of the bed, and an inch of castings are harvested from below by pulling a breaker bar across the large mesh screen which forms the base of the bed.

Because red worms are surface dwellers constantly moving towards the new food source, the flow-through system eliminates the need to separate worms from the castings before packaging. Flow-through systems are well suited to indoor facilities, making them the preferred choice for operations in colder climates.

Small scale

Demonstration home scale worm bin at a community garden site - painted plywood

For vermicomposting at home, a large variety of bins are commercially available, or a variety of adapted containers may be used. They may be made of old plastic containers, wood, Styrofoam, or metal containers. 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.

Some materials are less desirable than others in worm bin construction. Metal containers often conduct heat too readily, are prone to rusting, and may release heavy metals into the vermicompost. Some cedars, Yellow cedar, and Redwood contain resinous oils that may harm worms^[9], although Western Red Cedar has excellent longevity in composting conditions. Hemlock is another inexpensive and fairly rot-resistant wood species that may be used to build worm bins.^[10]

Bins need holes or mesh for aeration. Some people add a spout or holes in the bottom for excess liquid to drain into a tray for collection. Worm compost bins made from recycled or semi-recycled plastic are ideal, but require more drainage than wooden ones because they are non-absorbent. However, wooden bins will eventually decay and need to be replaced.

Small-scale vermicomposting is well-suited to turn kitchen waste into high-quality soil amendments, where space is limited. Worms can decompose organic matter without the additional human physical effort (turning the bin) that bin composting requires.

Composting worms which are detritivorous (eaters of trash), such as the red wiggler Eisenia fetidae, are epigeic (surface dwellers) together with symbiotic associated microbes are the ideal vectors for decomposing food waste. Common earthworms such as Lumbricus terrestris are anecic(deep burrowing) species and hence unsuitable for use in a closed system.^[11] Other soil species that contribute include insects, other worms and molds.^[12]

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