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Vermicompost (also called Vcompost, compost, vermicast, worm castings, worm humus or worm manure) is the end-product of the breakdown of organic matter by some species of earthworm. Containing water-soluble nutrients, microbes, and bacteria, vermicompost is one of the best, nutrient-rich organic fertilizer and soil conditioners available.[1] The process of producing vermicompost is called vermicomposting.

The earthworm species (or composting worms) most often used are Red Wigglers (Eisenia foetida). These species are commonly found in rich organic soils throughout Europe and North America and live in rotting vegetation, compost and manure piles. 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 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 your driveway on a rainy day. Small-scale vermicomposting is well-suited to turn kitchen waste into high-quality soil amendments, where space is limited. Worms can also convert matter more quickly and without the physical effort that composting requires.

Earthworms and bacteria are the major catalysts for decomposing the food waste in a healthy vermicomposting system. Other soil species that contribute include insects, other worms and molds.


  • Vermicast or worm castings - 100% excreta of worms after organic matter has been completely broken down through the worm's digestive tract
  • Vermicompost – a mixture of varying quantities of vermicast, compost and undigested organic matter.


Diagram of a household-scale worm composting bin

Vermicomposting bins (also known as worm bins) vary drastically depending on the desired size of the system. Garden-scale containers can be made out of bricks arranged in the shape of a box. Bins for an apartment or similar dwelling can be anything from reused plastic buckets to purpose-built commercial containers.

Other equipment and materials necessary for vermicomposting are: a large spoon to stir the bin’s contents; a strainer and a large bowl to strain the waste liquid and sludge; jars to store the liquid and/or to steep the solids to make ‘tea’.

Large scale[edit]

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 (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. When large scale windrows are fed on one side consistently, a wave motion is generated over time.

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 and are 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[edit]

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[2]. Metal containers often conduct heat too readily, are prone to rusting, and may release heavy metals into compost. Their quality and reliability can be verified by quality control systems.

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 of bedding 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, with bedding material. Then a layer of soil which organic matter is then added too. Another bin made in the same fashion can be stacked on top of a filled bin. Worms finish composting the materials in the bottom tray and then migrate to the one above. When a sufficient number of worms have migrated, the vermicompost in the bottom tray can be collected and should be relatively free of worms. These bins provide an easier method of harvesting[3].
  • 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 convenient.

Starting off[edit]

When beginning a vermicomposting bin, moist bedding is put into the bin and the worms are added. In hot climates, the bin is placed away from direct sunlight. Appropriate waste can be added daily or weekly. At first, the worms are fed at most half their body weight per day. After they have established themselves, they can be fed up to their entire body weight. It is best not to add new food on top of old food until the old food has been processed by the worms. However, new food can be added in a different location in the bin.


Bedding is the living medium and also a food source for the worms. It should be material high in carbon and made to mimic decaying dried leaves on the forest floor, the worms' natural habitat. The bedding should be moist (similar to the consistency of a wrung-out sponge) and loose to enable the worms to breathe and to facilitate aerobic decomposition of the food that is buried in it.

A wide variety of bedding materials can be used, including shredded newspaper (strips 1” wide or less), sawdust, hay, shredded cardboard, coir, burlap coffee sacks, peat moss, pre-composted (aged) manure, and dried leaves (oak leaves, which are high in tannic acid, should be avoided). Cat litter, and pet and human waste should not be used, because they may carry disease. Also, dogs are commonly given worming medications that can kill earthworms if dog waste is placed in the worm bin.

Most vermicomposters avoid using glossy paper from newspapers and magazines, junk mail, and shredded paper from offices, because they may contain toxins which may disrupt the system. Also, coated cardboard that contains wax or plastic, such as milk boxes, should not be used. Newspaper and phone books printed on regular, non-glossy paper with non-toxic soy ink are safe for use, and decompose relatively quickly.

Climate and temperature[edit]

Worms used in composting systems prefer temperatures of 55 to 70 degrees Fahrenheit (12-21 degrees Celsius). The temperature of the bedding should not drop below freezing or rise above 89.6 °F (32 °C). This temperature range means that indoor vermicomposting is suitable for homes in all but tropical climates.

The map of vermicomposters location data plots geographic data which shows which climates are suitable for worm composting.


Worms and other composting organisms have a preferred ratio of carbon to nitrogen (C:N), approximately 30:1. As some waste is richer in carbon and others in nitrogen, waste must be mixed to approximate the ideal ratio. "Brown matter", or wood products such as shredded papers, is rich in carbon. "Green matter", such as food scraps, has more nitrogen, which is related to the amount of protein in the waste.[4]If the waste is mostly vegetable and fruit scraps, and does not regularly include animal products or high-protein vegetable foods like beans, the resulting vermicompost and waste liquid will be low in nitrogen.


Kitchen waste suitable for worms includes coffee grounds and paper filters, tea bags, plate scrapings, rotting fruits and vegetables (including citrus fruit but not citrus peel), fruit and vegetable peels and ends, leftovers, moldy bread, etc. These materials can be raw or cooked. They do not have to be ground up, as the micro-organisms in the bin will gradually soften them. However, chopping fruit and vegetable scraps into smaller pieces will speed the composting process. If a large quantity of dry food (e.g., moldy bread) is added and covered with bedding, pour a little purified Template:Verify credibility water over the bedding to moisten the mixture. Freezing food before giving it to the worms helps them digest it because the cell walls are weakened and the food decomposes more rapidly.

If too much kitchen waste is added, the bin mixture putrifies before the worms can process it and becomes harmful to the worms. High-protein foods like beans are particularly susceptible. For these reasons many vermicomposters limit their mix to only include fruit and vegetable matter, avoiding grains, proteins or prepared food scraps altogether. Check the bin at least once a week, give the materials a stir to oxygenate, and add bedding if the bin appears too moist.

Soft wastes from the garden such as carrot tops and tomato leaves are suitable foods. An occasional sprinkling of garden soil in the bin gives the worms the grit they need to digest food. It's not harmful to throw in an entire plant, such as a tomato plant at the end of the season, but the worms will not process the woody parts or large roots and these will have to be hand-removed later from the finished vermicompost.

Compostable plates, cups, etc. are also suitable food, but in small bins they should be torn first into smaller pieces so as not to block oxygen flow.

Manure from most farm animals can be used, but chicken manure will heat up the worm bin. All manure should be aged and hot composted to kill weed seeds.


Grass clippings and other products sprayed with pesticides should be avoided.

Although worms can digest proteins and fats in meat scraps, these materials can attract scavengers. Too much oil or fat can hinder the breathing of the worms, as they breathe through their skin. Worms cannot break down bone and are said to dislike highly spiced foods and salt.[5] Adding meat and dairy products increases the difficulty of maintaining a healthy, low-odor vermicomposting mix, and is usually not recommended. Small amounts from occasional plate scrapings are ok. However, if the amount of meat or dairy added is small relative to the volume of the bin, such material may be added[6].

Acidic foods (tomatoes, citrus), starchy foods (bread, rice), garlic and onions should only be added in moderation. Large amounts of these materials can change the balance of the system.

Bin maintenance[edit]

Worms and composting microorganisms require oxygen, so the bin must "breathe". This can be accomplished by regularly removing the composted material, adding holes to the 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 and creating a toxic environment for the worms.

The moisture level and oxygen flow in a home worm bin should be checked at least once a week.

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, depending on the foods used, may require sprinklings of water to keep the bedding moist.

The pH should be slightly alkaline. Alkalinity can be increased by occasionally adding a handful of calcium carbonate, sold as "garden lime." (Do not confuse calcium carbonate with regular lime (Calcium oxide), which is far too alkaline and will kill worms.) Overly acidic compost can also be easily corrected by adding finely crushed eggshells, which many kitchen-scrap vermicomposters include along with vegetable matter as part of a balanced mix.[7]

Adding many citrus peels can hinder the worms, but probably due not to acidity but to d-limonene, a fragrant chemical present in the rind of citrus fruits.[8] Coffee grounds have sometimes been blamed for acidity, but analysis shows they are only mildly acidic, with a pH of 6.2.[9]


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, rotating around the bin to give the worms time to decompose the food in the previously fed pockets. The top layer of bedding is replenished as necessary.

Vermicomposters often use a combination of both methods. Sometimes unburied food can attract fruit flies, so food should be buried under at least one inch of bedding material.


Vermicompost is ready for harvest when it contains few to no scraps of uneaten food or bedding. Even a properly composted mixture will contain visible large items that should be discarded, such as peach pits, glassine-like sheets from melon skins, and twigs.

There are several methods of harvesting, depending on the purpose for which the vermicompost will be used, and whether or not the composter wishes to salvage as many worms and worm eggs as possible from the vermicompost.

Vermicompost properties[edit]

Vermicompost is richer in many nutrients than compost produced by other composting methods. It is also rich in microbial life which helps break down nutrients already present in the soil into plant-available forms. Unlike other compost, worm castings also contain worm mucus which keeps nutrients from washing away with the first watering and holds moisture better than plain soil. For this reason, some fruit and seed pits are reported to germinate in vermicompost easily. Vermicompost made from ordinary kitchen scraps will contain small seeds, especially those of tomatoes, peppers, and eggplants, that may sprout weeks later.


Vermicompost benefits soil by

  • improving its physical structure;
  • enriching soil in micro-organisms, adding plant hormones such as auxins and gibberellic acid, and adding enzymes such as phosphatase and cellulase;
  • attracting deep-burrowing earthworms already present in the soil;
  • improving water holding capacity;
  • enhancing germination, plant growth, and crop yield; and
  • improving root growth and structure.

Uses as fertilizer[edit]

Vermicompost is used as a fertilizer in three ways:

  • The vermicompost itself can be mixed into the soil
  • Vermicompost can be used to make compost tea (worm tea), by mixing some vermicompost in water and steeping for a number of hours or days. Its microbial activity is greater if it is aerated during this period. The resulting liquid is used as a fertilizer.
  • The dark brown waste liquid, or leachate, that drains into the bottom of some vermicomposting systems as water-rich foods break down, is also excellent as fertilizer.

The pH and nutrient contents of these fertilizers varies, depending on the food fed to the worms and whether or not lime has been added to the system. pH and nitrogen, phosphorus, and potassium (NPK) measurements should be taken periodically to determine the fertilizer composition before use. Home kits for testing are sold in hardware stores and nurseries. In the USA, land grant universities may be able to test soil..


Odor, usually due to overabundance of "greens" (wet waste) in the bin, results from too much nitrogen combining with hydrogen to form ammonia. To neutralize the odors, add a fair amount of shredded newspaper or other "browns" to the mix to absorb excess moisture, remove the smelly waste, and stop adding food to the bin until a substantial portion of the uneaten food has been turned into compost. The carbon will balance the nitrogen and form a compound that is not smelly. The higher level of carbon means that decomposition will be slower. Also, always add new material deep in the bin to disallow access to would-be pests. Consistently doing so will greatly reduce any nuisance from odor and undesirable organisms.

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 avoided if a sealed bin is used where the pests cannot access the material, although many proponents recommend having ample access to air. This promotes natural decomposition, as worms and beneficial bacteria require oxygen.

In warm weather, fruit and vinegar flies breed in the bins if the food is not thoroughly covered with bedding. Some people advocate putting a small jar containing vinegar inside the bin as a trap for the flies.

See also[edit]

External links[edit]


  1. Coyne, Kelly and Erik Knutzen. The Urban Homestead: Your Guide to Self-Sufficient Living in the Heart of the City. Port Townsend: Process Self Reliance Series, 2008.
  2. "Compost Worms". Retrieved 2008-02-12. 
  3. "Build a Vermicompost Bin". Retrieved 2009-2-3. 
  4. Richard, Tom; Nancy Trautmann. "C/N Ratio". Cornell composting: composting in schools. Cornell university college of agriculture and life sciences. Retrieved 2007-07-29. 
  5. Fact Sheet: Building a Worm Farm ABC Gardening Australia. Retrieved 2008-08-24
  6. Can you put meat in a worm bin Retrieved 2009-02-22
  7. Dickerson, George W. 2001. Vermicomposting Guide Book published by New Mexico State University. Online:
  8. In her book, Worms Eat My Garbage, (Kalamazoo, MI: Flower Press, 1997), p. 64, pioneering vermicomposter Mary Appelhof says that another science teacher's ninth-grade student did a science project that identified limonene as the toxin. Appelhof was skeptical but realized that the student probably had a parent who worked at a nearby Dupont Chemical Company research facility with the ability to do the tests.
  9. Soil and Plant Laboratory Inc., Bellevue, WA. (2005). "The Starbucks coffee compost test". Sunset magazine. Retrieved 2007-07-29.