What is Vermicomposting & How Does it Work?

Composting allows homeowners to turn their yard and garden waste into an organic soil amendment full of nutrients and beneficial microorganisms through natural biological processes.

While this works well for homeowners with usable space outside in their yard, it presents challenges to apartment dwellers or those with limited outdoor space.

Those challenges can be circumvented through vermicomposting, a composting process in which worms break down food and kitchen waste into vermicast, often allowed to happen indoors.

This guide will explain what vermicomposting is, how it differs from traditional composting, the benefits of vermicomposting, and the supplies and steps needed to start your own worm bin.

What Is Vermicomposting?

Vermicomposting is a variation of traditional composting where microorganisms and worms break down organic materials into worm castings or vermicast, a nutrient-rich natural fertilizer, and soil amendment.

Microorganisms begin to digest and decompose the food waste, and then the worms consume the microorganisms and the partially decomposed food, excreting the broken-down byproduct known as castings.

The castings are then used as a soil amendment like traditional compost. Compared to ordinary garden soil, worm castings contain five times more nitrogen, seven times more phosphorus, and eleven times more potassium.

Worm Castings in Soil

They are rich in humic acids and improve the structure of the soil like traditional compost.

Vermicomposting Versus Traditional Composting

Technically, vermicomposting is classified as a method of composting, albeit there are some significant differences between vermicomposting and more conventional methods.


  • Food and kitchen items are left to break down with little intervention from the gardener/homeowner.
  • Is considered a “cold” process since there is no noticeable heat generated as the materials are broken down.
  • Relies on a combination of micro and macro-organisms, specifically worms, instead of heat to drive the process.
  • Can’t kill weed seeds if they are present in the bin due to the lack of high temperatures within the pile.
  • The finished product generally has lower carbon-to-nitrogen ratio because of the mixture of items in the bin. Less carbon-rich materials are needed for the process, which equates to more nitrogen in the finished product versus traditional compost.
  • Can take up to 6 months for the finished compost.


  • Requires manual labor to keep the process moving forward by turning the pile periodically.
  • Is typically a “hot” process that is more active than cold composting. The conditions are carefully maintained to keep the process working efficiently, raising the internal temperature of the pile to 141-155℉ for optimum decomposition.
  • Depends on the heat generated by microorganisms (mainly bacteria) to convert the organic waste in the pile or bin to finished compost.
  • Takes 6 to 8 weeks for finished compost under optimal conditions.

Benefits of Vermicomposting

Benefits of Vermicomposting

The benefits of turning waste into compost and then applying it to soil are no secret.

A quick internet search or a conversation with a composting aficionado provides plenty of information, but the gains run far deeper for both your soil and the environment.

Compost helps to improve soil structure and drainage when added to garden soils, flowerbeds, and agricultural fields.

Using compost as a soil amendment also aids in environmental sustainability by reducing erosion and nutrient leaching and lessening the application of water as well as synthetic chemical inputs such as fertilizers and pesticides.

Making compost allows you to know exactly what materials have gone into the process, ensuring the highest quality.

Vermicomposting embodies the benefits of traditional composting while having a few benefits specific to the process itself.

  • Diverts kitchen and food waste from landfills, reducing methane.
  • A worm bin can be kept inside, allowing the process to continue all year long, even during the colder winter months.
  • Uses less space than traditional composting.
  • Less labor intensive because it’s a cold process.
  • Very little odor comparatively.
  • Vermicast is richer than conventional compost in beneficial soil microbes, polysaccharides, proteins, and other nitrogenous compounds.

Supplies Needed to Begin Vermicomposting

While similar in process to traditional compost bin or pile, vermicomposting has different required supplies needed to get started. You need a container or bin, bedding for the worms, the worms themselves, and food scraps.

Worm Bin

Plastic totes, wooden boxes, and commercial stacking worm towers are the most commonly used materials for worm bins.

Plastic totes and wooden boxes may require some modification to add ventilation and drainage holes but are popular because they can be customized to the space. If you are making your own bin remember to choose opaque materials, and don’t forget your container needs a lid!

Prefabricated worm towers are ready to go out of the box but are more expensive and aren’t easily customizable. They are well-liked by some homeowners because harvesting the finished vermicast is much simpler.

What size bin you use for vermicomposting depends on the amount of waste generated by your household in a week. A general rule of thumb is for every pound of waste created, you need 1 cubic foot of space in the bin.



There are a couple of species of worms that are suitable for worm bins, with red worms being the most popular.

Also known as red wigglers, branding, or manure worms, Eisenia foetida are about 4 inches long with mainly a red body and a yellow tail. These types of worms live in the organic material on top of the ground, working their way through decomposing leaves and decaying plant matter.

While red worms can be gathered from the yard, it’s best to start by buying your initial supply. They can be purchased from a variety of online retailers.

Do not use common earthworms that come to the surface of the ground after a rain; they need soil to live in and the cool temperatures that come with burrowing down beneath the topsoil.


Providing the right bedding in your worm bin is critical to creating an environment for the vermicomposting process to occur successfully.

The purpose of bedding materials in the bin is to simulate conditions similar to the worms’ natural habitat. They burrow down in the bedding to stay out of the light, they breathe moisture from the bedding through their skin, and they use the bedding materials as a food source.

Many types of carbon-rich materials — think wood-based or fibrous items — are great options to use, especially if you can mix materials to provide variety.

It’s best if they are non-toxic, don’t contain ingredients or sharp pieces that can irritate the worm’s skin, can easily be eaten, are airy, and hold moisture well. If possible, they should be soft and preferably in smaller pieces.

Be careful to not dump a large amount on top that can cut off the air supply to the tunnels, creating an anaerobic environment.

Best Materials for Bedding

  • Corrugated brown cardboard is one of the most commonly used materials for worm bedding. It’s easy to procure, inexpensive, and the corrugation allows for incredible air movement through the substrate. Avoid using cardboard that has colored ink printed on it, and try to tear it into small pieces before adding it to the worm bin.
  • Coconut coir is a popular growing media in hydroponics systems. Comprised of the brown and white fibers found between the shell and the outer coating of a coconut seed, it is similar in texture to peat moss and holds approximately 8 to 10 times its weight in water. Coconut coir naturally resists compaction, has a pH close to neutral, and promotes the growth of beneficial bacteria due to the presence of lignins.
  • Shredded copy, printer, or newspaper works well as bedding for your worm bin, especially if it doesn’t contain colored ink. Avoid bleached white office or computer paper and glossy papers if possible. Run the paper through a shredder or cut/tear it into small pieces before use.
  • Peat moss is commonly used in container gardening. It is light and retains 10 to 20 times its weight in water while still draining efficiently. Peat moss can be used if there are no added materials or chemicals; if anything else is listed on the package, avoid using it for worm bedding.
  • Half-finished compost makes excellent bedding material because it contains microorganisms to break down the food waste, as well as acting as an appropriate food source for the worms.
  • Partially decomposed yard waste, such as autumn leaves, can also be used. If possible, allow them to sit over the winter before adding them to the bin. Check carefully for pests such as slugs or snails, and then shred into smaller pieces.
  • Straw is easy to find, lightweight, and inexpensive. Make sure the straw is weed-free, and then add chopped-up straw to the worm bin.


Worms have a gizzard, much like birds, and require some sort of grit to help break up food particles.

Every couple of months, add one of the following materials to the worm bin to aid in digestion: sand, pulverized egg shells, vermiculite, garden soil, or calcium powders.

Kitchen or Food Scraps

Kitchen or Food Scraps

Lastly, you need the organic materials the worms break down into worm castings.

Food and/or kitchen scraps are the preferred option and are partly why worm bins are commonly found inside the home.

It’s important that care is taken when choosing what scraps to add to the bin:

  • Fruit and vegetable scraps and/or coffee grounds are the top three items encouraged for vermicomposting.
  • Avoid adding acidic or irritating food items such as citrus, onions, and hot peppers.
  • Keep in mind a worm’s body is essentially a mucous membrane; anything that stings or irritates your eyes causes your worms pain.
  • Fatty items such as meat, dairy, and cooking oils should be discarded in the trash instead of being added to the bin since they cause odors and may attract pests.
  • Bread, rice, or beans, ferment or mold when added to your bin in large quantities, causing distress to the worms.

Setting Up a Worm Bin

After determining the size worm bin needed and gathering all of the necessary supplies, it’s time to get the bin set up, and the process started!

If timing allows, set up the bin, bedding, and food about two days before you add the worms. In this time span, the moisture level will come to an equilibrium, and the microbes will begin breaking down the food waste.

  1. Start by covering the bottom of your bin with a layer of shredded newspaper or other bedding material. Fluff it up with your hand to help minimize compaction.
  2. Add the waste in a fairly even, light layer across the bedding at a rate of about a pound of food per pound of worms.
  3. Add another layer of dry, shredded bedding, entirely covering the food waste. Make sure to fluff it well.
  4. Cover and let the bin sit for a day or two. Periodically check inside to see if moisture from the food has spread to the bedding, making it slightly moist. There should be no liquids pooling within the bin. If the bedding is dry after a day or two, add a small amount of water, mixing the items in the container.
  5. Once the bedding is sufficiently wetted, pull back the top layer, add your worms and any other organic bedding you’d like to add (such as the materials your worms came in or old worm castings), and then cover with the top layer again.
  6. Tightly close the bin, and place it somewhere out of the direct sunlight where the ambient temperatures stay between 50 and 80℉.
  7. For the first night, it might be worthwhile to shine a line directly on the bin to keep the worms from trying to escape. They will take a day or two to acclimate to their new space; their disdain for light will keep them contained.

Maintaining a Worm Bin

After the initial setup, there are some basic maintenance items you’ll need to perform to keep the worms happy and working efficiently.

Adding Food Waste

On average, healthy worms consume approximately half their weight in food daily, continuously eating their way through the food and bedding in a worm bin.

This makes it necessary to periodically add new food waste to the bin to replenish their food source. Indoor bins should be fed weekly; outdoor worm bins should be fed every 2 to 3 weeks but can be fed a larger amount at each feeding.

To facilitate the vermicomposting process, you can freeze and thaw food before adding it to the bin or allow food to sit for a couple of days to naturally begin to decompose. This makes it easier for the worms to start consuming it.

Moisture & Oxygen

There is a delicate balance between the moisture and oxygen levels within your worm bin, and one of the key components to manage.

When the bedding is overly wet, the water molecules will fill all of the pore space between the materials, as well as the worm tunnels, pushing oxygen out. If there is too much oxygen, or air circulation, in the worm bin, the materials will dry out too much, negatively impacting the worms.

Make sure the food and bedding in your bin are always consistently moist, similar to a damp sponge.

The food waste added to the container will typically be very high in water content, providing the worms with all the moisture they need. If water pools or collects within the bin, add a couple of handfuls of fresh, dry bedding.


The best way to gauge if your worm bin is at the right temperature is to take a minute and determine if you’re too hot or too cold.

Ideal conditions for vermicomposting are between 60 and 80℉, similar to the temperature most people prefer.

At temperatures lower than 60℉ and higher than 80℉, the worms will decrease the amount of food they eat, and reproduction will slow down. In turn, the vermicast created will decrease.

If temperatures drop below 40℉ or climb higher than 95℉, the worms will die.


Bedding acts to absorb excess moisture from the food scraps and increase airflow in the bin, so it needs to be replenished often.

It’s recommended to add fresh bedding every time your worms are fed. Covering the added food with a generous layer of dried, shredded bedding also keeps flies and odors to a minimum.


Worms highly dislike sunlight or any artificial light and will naturally move away from light cast onto the worm bin.

Keep the container in a dark location other than when you are adding food or bedding to keep worm activity at its highest.

Vermicomposting Tips

To keep your worm bin functioning at its optimum level, it’s best to heed the following tips or tricks.

  • Don’t use garden soil as bedding. It is too heavy and will compact within the bin, preventing the worms from burrowing through it.
  • Err on the side of underfeeding worms versus overfeeding. Excess food will begin to rot, depleting the oxygen in the bin.
  • Avoid using insecticides in close proximity to your worm bin to prevent any chemical drift and resulting contamination.
  • Do not add any fresh animal manure to the bin. It raises the internal temperature too much, resulting in the death of your worms.
  • Regardless if your bin is outside or kept inside, keep cats away from it, preventing them from using it as a litter box. The ammonia in urine will kill your worms.
  • If you or anyone in the household is allergic to molds and/or mildew, keep the bin away from your living area or even outside of the home. They are a natural part of the process and unavoidable.

Harvesting Finished Compost

Harvesting Finished Compost

After setting up your worm bin, it will take approximately 4 to 6 months for the worm castings to be ready for the first harvest.

They are ready to harvest and use when the bin looks like it contains little or no scraps of uneaten food or bedding. The finished product will be very dark and rich in color.

Removing the finished castings from the bin can be accomplished in a couple of different ways.

  • The easiest way to harvest the compost is to simply reach in and grab handfuls of the castings from the bin. You can add worms and all to your garden or pick the worms out to add the castings to your potted plants.
  • Worms dislike light intensely, so it can be used to your advantage. Remove the lid on the worm bin and shine a light directly onto the castings. The worms will move toward the bottom of the container to get away from the light, and the castings can be removed from the top.
  • Another way to harvest the materials is to move the finished castings to one side of the worm bin and add fresh, dry bedding material to the other side. After a couple of days, the worms will migrate to the side with the fresh bedding, allowing you to harvest the castings.
  • Dump all of the bin out onto a clean, dry tarp set out in the sunshine, spreading the material out. Then make a couple of mounds or pyramids of the worm castings. The worms will move to the mounds in an attempt to get out of the sunlight. After a while, brush the outer layer off the piles, causing the worms to bury deeper. Continue until you’re left with a ball of worms that can be used to start a new bin.


Vermicomposting is a fantastic alternative to traditional composting if you’re tight on space, lack a yard, or are not ready for the demands of a regular composting bin or pile!

Microorganisms and worms break down food waste to create vermicompost, or worm castings, a nutrient-rich organic soil amendment that is usable in container plants or outside to amend your garden soil.