Vermicompost is the result of a breaking down process that uses certain types of worms, such as red wigglers, white worms, and other earthworms. These worms help mix decomposing vegetable or food waste, bedding materials, and vermicast. This process is called vermicomposting. Raising worms for this purpose is known as vermiculture.

Vermicast, also referred to as worm castings, worm humus, worm poop, worm manure, or worm faeces, is the final product of earthworms breaking down organic matter. These excreta contain fewer contaminants and more nutrients than the original materials before the vermicomposting process.

Vermicompost includes water-soluble nutrients that can be collected as vermiwash. It is a valuable, nutrient-rich organic fertilizer and soil conditioner. It is used in gardening and in sustainable, organic farming practices.

Vermicomposting can also be used to treat sewage. A variation of this process, called vermifiltration (or vermidigestion), helps remove organic matter, harmful germs, and oxygen demand from wastewater or directly from blackwater from flush toilets.

Overview

Vermicomposting is becoming more common in both large-scale and home settings because it helps break down organic waste faster than traditional composting. When used with manure, vermicomposting creates products with less salt and a more balanced pH.

The most commonly used earthworms for vermicomposting are red wigglers (Eisenia fetida or Eisenia andrei). Other types, such as European nightcrawlers (Eisenia hortensis, also called Dendrobaena veneta) and red earthworms (Lumbricus rubellus), can also be used. Experts recommend red wigglers because they eat quickly and reproduce fast. European nightcrawlers are sometimes called dendrobaenas, dendras, Dutch nightcrawlers, or Belgian nightcrawlers.

Vermicompost is a type of organic fertilizer and soil conditioner made from nutrients that are easy for plants to use. It contains water-soluble nutrients. Worm castings, which are the waste produced by earthworms, are also used as fertilizer. Earthworms grind and mix minerals into simple forms, making it easier for plants to absorb them. The digestive systems of earthworms support helpful microbes that improve soil health. The part of soil that passes through an earthworm’s digestive system is called the drilosphere.

Vermicomposting is often used in permaculture, a method of growing plants in a sustainable way.

Vermiwash is a liquid made from the liquid part of vermicompost. It contains enzymes like proteases, amylases, urease, and phosphatase. Studies show that vermiwash includes bacteria that add nitrogen to soil, such as Azotobacter sp., Agrobacterium sp., and Rhizobium sp., as well as bacteria that help release phosphorus. Tests in laboratories have shown that vermiwash can help plants grow better.

Design considerations

Not all worms can make compost, but some types are better suited for this task. Vermicompost worms are usually surface-dwelling. The most common species used for composting are:

• Eisenia fetida (Europe), also called red wigglers or tiger worms. This species is closely related to Eisenia andrei, which is also useful for composting.
• Eisenia hortensis (Europe), known as European nightcrawlers. These worms prefer materials with a high carbon-to-nitrogen ratio.
• Eudrilus eugeniae (West Africa), called African nightcrawlers. These are useful in tropical climates.
• Perionyx excavatus (South and East Asia), also called blueworms. These are used in tropical and subtropical regions.
• Lampito mauritii (Southern Asia), used locally in some areas.

These species are often found in organic-rich soils in Europe and North America. They live in decaying plants, compost, and manure piles. Because they stay near the surface and eat decomposing plant material, they can easily live in the controlled environment of a worm bin. However, some species are invasive in certain areas and should be avoided (see information about invasive earthworms for details).

Composting worms can be purchased online, from nurseries, or from fishing shops where they are sold as bait. They can also be collected from compost or manure piles. These worms are different from the ones found in regular soil or on wet pavement.

The following species are not recommended for composting:

• Lumbricus rubellus and Lumbricus terrestris (Europe). These worms dig deep underground and come up to eat. They are not well-suited for shallow compost bins and are invasive in North America.

Large-scale vermicomposting is practiced in countries like New Zealand, Canada, Italy, Japan, India, Malaysia, the Philippines, and the United States. Vermicompost can be used for farming, gardening, landscaping, making compost tea, or for sale. Some operations also produce worms for fishing bait or home composting.

There are two main methods for large-scale vermicomposting: windrow composting and raised beds. In windrow composting, organic material is arranged in rows for worms to feed on. Worms stay in the rows if conditions are right, such as proper moisture, temperature, and a balanced mix of materials. Windrows are often placed on concrete to manage liquid runoff.

The largest vermicomposting operation by volume is MyNoke in New Zealand. Since 2007, it has processed over 1.4 million tonnes of organic waste. Windrow turners, developed by Fletcher Sims Jr. in Texas, help farmers manage dairy waste in a sustainable and cost-effective way.

The second method is the raised bed or flow-through system. In this system, worms are fed food across the top of the bed, and castings (worm waste) are collected from the bottom through a mesh screen. This system works well for indoor composting and is preferred in colder climates because it avoids the need to separate worms from castings before packaging.

For home vermicomposting, many types of bins are available or can be made from materials like plastic containers, wood, Styrofoam, or metal. The design of a bin depends on where it will be stored and how it will be fed. Some materials are less ideal: metal bins can rust and release harmful metals, Styrofoam may release chemicals, and certain woods like cedar or hemlock can affect worm health. Wooden bins may eventually decay and need replacing.

All bins need holes or mesh for air circulation. Some people add a spout or holes at the bottom to collect excess liquid. Plastic bins are popular because they are easy to clean but require more drainage than wooden ones. Wooden bins are more absorbent but may need to be replaced over time.

Small-scale vermicomposting is useful for turning kitchen waste into high-quality soil amendments, especially in limited spaces. Worms can break down organic matter without the need for frequent turning, which is required in traditional composting.

Worms used in composting, like red wigglers (Eisenia fetida), are surface-dwelling and work with microbes to break down food waste. Common earthworms like Lumbricus terrestris dig deep underground and are not suitable for closed systems. Other decomposers include insects, other worms, and fungi.

Vermicomposting methods may vary based on climate. Large-scale systems must monitor temperatures, as heat from decomposing materials can harm worms. Redworms (Eisenia fetida, Eisenia andrei, and Lumbricus rubellus) work best at temperatures between 15–25°C (59–77°F) and can survive at 10°C (50°F). Temperatures above 30°C (86°F) may harm them. This means redworms can be used indoors in most climates except tropical ones. Worms like Perionyx excavatus are better suited for warmer areas. If a worm bin is placed outside, it should be in a shaded, sheltered spot and insulated during cold weather.

Feedstock

Vermicomposting can handle most food waste, but meat and dairy products may rot and attract pests in outdoor bins. Green waste should be added in small amounts to prevent the bin from overheating.

These systems typically use kitchen and garden waste, which is broken down by earthworms and other microorganisms. This includes:

• All fruits and vegetables (including citrus, but only a little)
• Vegetable and fruit peels and ends
• Coffee grounds and filters
• Tea bags (even those with high tannin levels)
• Grains such as bread, crackers, and cereal (including moldy or stale items)
• Eggshells (washed clean)
• Leaves and grass clippings (not treated with pesticides)
• Newspapers (most inks used are not harmful)
• Paper towels (not used with cleaners or chemicals)

Vermicomposting systems require large amounts of food waste. Current systems use waste from:

• Dairy cow or pig manure
• Sewage sludge
• Brewery waste
• Cotton mill waste
• Agricultural waste
• Food processing and grocery waste
• Cafeteria waste
• Grass clippings and wood chips

Harvesting

The speed of composting depends on the climate and the composting method used. Signs that compost is finished include having a room temperature, dark color, and being as wet as a damp sponge. Near the end of the process, bacteria may slow down or stop breaking down food. Some solid organic material might still be in the compost at this stage, but it can continue to break down over the next few years unless removed. After compost is finished, it should be left to cure so that acids can be removed over time, making it more neutral. This curing process may take up to three months and helps the compost become more uniform in size. Keeping the compost elevated off the ground can help stop unwanted plants from growing. The compost should stay slightly damp and be aerated, but it does not need to be turned. The curing process can happen in a storage bin or on a tarp.

Vermicompost is ready to use when there are very few or no pieces of uneaten food or bedding left. Small-scale systems use several harvesting methods, including "dump and hand sort," "let the worms do the sorting," "alternate containers," and "divide and dump." These methods vary in how much time and effort they require and whether the person wants to save as many worms as possible from being included in the harvested compost.

The pyramid method is often used in small-scale vermicomposting and is considered the easiest way to harvest compost from single-layer bins. In this method, compost is divided into large clumps that are returned to the bin for further breakdown, while the lighter parts are used for the next steps. The lighter mix is placed in small piles on a tarp in sunlight. Worms naturally move to the bottom of the pile. After a few minutes, the top of the pile is removed repeatedly until worms are visible again. This process repeats until the pile is mostly made of worms.

During harvesting, it is possible to separate eggs and cocoons and return them to the bin so new worms can hatch. Cocoons are small, lemon-shaped, yellowish objects that can be seen without a magnifying tool. Each cocoon can contain up to 20 worms, though 2 to 3 is most common. Cocoons can stay inactive for up to two years if the environment is not suitable for hatching.

Properties

Vermicompost has more nutrients than compost made by other methods. Research shows it has performed better than a commercial plant medium with added nutrients. However, magnesium levels and soil pH needed adjustments in some cases.

In one study, homemade vermicompost made in backyards had less microbial life, less soil activity, and lower ryegrass growth compared to compost made by cities.

Vermicompost is rich in tiny living organisms that change nutrients in the soil into forms plants can use. Worm castings, which are the waste of worms, also contain mucus that helps keep nutrients from being washed away and holds more moisture than regular soil.

Studies have found that vermicompost has more total nitrogen, more available nitrogen and phosphorus, and less potassium. It also removes heavy metals from sludge and soil. Research has shown that this process reduces how easily plants can take up heavy metals.

Benefits of vermicomposting

• Helps air move through soil
• Adds helpful microbes to soil (such as enzymes like phosphatase and cellulase)
• Soil with worm castings has 10 to 20 times more microbes than the soil and organic matter worms eat
• Attracts earthworms that dig deep into the soil
• Helps soil hold more water

• Helps seeds grow into plants and improves plant growth and crop harvests
• Supports root and plant development
• Adds helpful soil organisms (such as plant hormones like auxins and gibberellic acid)

• Reduces the amount of waste sent to landfills
• Keeping biowaste out of recycling bins prevents it from mixing with other recyclables in single-bin systems
• Creates jobs that don’t require special skills in the local area
• Doesn’t require a lot of money to start and uses simple technology, making it practical for areas with less developed farming

• Recycles waste where it is produced
• Large systems may use temperature control and machines to collect worms, but other parts are simple and last a long time
• Reduces harmful gases like methane and nitric oxide that are made in landfills or when waste is burned.

Uses

Vermicompost can be mixed directly into the soil or combined with water to create a liquid fertilizer called worm tea.

The light brown liquid, known as leachate, that collects at the bottom of some vermicomposting systems is different from worm tea. Leachate is a byproduct that forms when water-rich foods break down and may contain harmful microorganisms or toxins. It should be thrown away or returned to the bin only when additional moisture is needed for further processing.

The pH, nutrient levels, and types of microbes in these fertilizers depend on the materials given to the worms. Powdered limestone, which is also called calcium carbonate, can be added to the system to increase the pH.

Operation and maintenance

When a bin is closed, it should have no smell. When opened, it should have little or no smell, and any smell should be earthy. The type of composted material added to the bin can affect the smell. A bin that smells strongly may be unhealthy, possibly because there is not enough oxygen. Worms need oxygen from the air. Oxygen can be added through airholes in the bin, by stirring the contents occasionally, or by removing some material if it becomes too deep or too wet. If the bin becomes too wet and decomposition happens without oxygen, the bin may start to smell like ammonia.

Moisture in the bin should be kept above 50%, as lower levels can harm the worms and increase their chances of dying. The best moisture range is between 70% and 90%, with 70% to 80% being ideal for composting. If decomposition becomes anaerobic, steps must be taken to fix the problem. First, stop adding wet food scraps. Second, add dry materials like shredded newspaper to the bin and mix them well to reduce moisture.

Pests like rodents and flies are attracted to certain materials and smells, especially large amounts of kitchen waste, such as meat. Using meat or dairy products in the bin increases the risk of pests.

Predatory ants can be a problem in some African countries.

In warm weather, fruit and vinegar flies may lay eggs in the bin if fruit and vegetable waste is not covered with bedding. To prevent this, cover the waste with at least 5 centimeters (2.0 inches) of bedding. Keeping the bin’s pH close to neutral and ensuring the bedding is moist but not dripping water can also help avoid pests.

Worms usually stay in the bin, but they may try to leave when first added or after rain when outdoor humidity is high. Providing good conditions in the bin and using a light above the bin when adding worms can help stop this.

Commercial composters test their products to ensure quality and consistency. Small-scale or home systems use varied materials, so the levels of nitrogen, phosphorus, and potassium (NPK) in the compost may vary. Testing NPK levels before using the compost or compost tea in a garden can be helpful.

To avoid over-fertilizing plants, vermicompost can be diluted by mixing 50 parts compost with 50 parts water, or mixed 50:50 with potting soil.

The mucous layer around worm castings allows nutrients to be released slowly, meaning not all nutrients are added at once. This slow release reduces the risk of burning plants, which can happen with overuse of commercial fertilizers.

Application examples

Vermicomposting is commonly used in North America to process food scraps at institutions like hospitals, universities, shopping malls, and correctional facilities. This method helps recycle organic materials on-site at a medium scale, such as food waste from universities and shopping malls. It is chosen because it is better for the environment or to lower costs for removing waste.

Starting on July 20, 2020, the government of Chhattisgarh, India, began purchasing cow dung under the "Godhan Nyay Yojana" program. The cow dung collected through this program will be used to make vermicompost fertilizer.