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The Handbook

Vermicomposting 101

Vermicomposting is the art of employing composting worms (Eisenia fetida) to convert food waste into a biologically rich material that plants thrive on. Whether you have a garden or not, this method of managing food waste is easy and accessible to anyone anywhere.

Food is the single largest category of material placed in municipal landfills and represents wasted nourishment that could have helped feed families in need. Additionally, water, energy, and labor used to produce wasted food could have been employed for other purposes. Effectively reducing food waste will require cooperation among federal, state, tribal and local governments, faith-based institutions, environmental organizations, communities, consumers, and the entire supply chain.
— U.S. Food & Drug Administration

We raise and extract food from the earth to consume it for energy to live our lives. When we fail to consume some part of the food we harvest it becomes "waste" which is discarded in a landfill where the remaining nutrients are no longer accessible to the soil or us. We are essentially throwing away tons of free nutrients that we and this planet depend on so we can buy bagged fertilizers instead. These bagged fertilizers then fail to penetrate into over-farmed, bacterially deplete, compacted soils and slide over the earth and straight into the ocean where they were never intended to go. The math really is simple.

With its ease of use and accessiblity vermicomposting gives anyone the ability to convert their household food waste into nutrients that can be cycled back into the soil. It can be done anywhere - an apartment, townhome, farmhouse, trailer, yurt, or in an HOA restricted home. If you don't have a garden to use the castings on donate it to a community garden, friend, family member, or package it in cute little tea bags to sell for some side income.

Purpose

To feed kitchen and garden food waste directly to composting worms within a contained space where they process and output the waste as castings (aka worm manure). These castings can then be applied to the garden where they supply plants with beneficial bacteria and nutrients in a form the plants can readily access. This reduces the financial and economic dependency on out-sourced fertilizers and amendments while reducing the amount of methane-emitting food waste being dumped into municipal landfills.

How It's Different Than Composting

close up of Eisenia fetida red wriggler composting worm

Much like composting vermicomposting requires a balance between carbon ("browns") and nitrogen ("greens"), oxygen, and a correct amount of moisture. Regular composting or aerobic composting is primarily bacterially dependent. This naturally-occuring aerobic bacteria is what attracts numerous organisms to the pile, including earthworms, to assist in the decomposition process. Vermicomposting is slightly different in that the combination of carbon, nitrogen, and moisture occurs in a contained area (usually a bin) and rather than wait for the bacteria to summon the organisms responsible for the breakdown we put them directly in an enclosed bin, skipping the wait, and providing us with pure castings. These organisms are Eisenia fetida, red wriggler composting worms.

Worm Basics

closeup of red wriggler in composting bin

Anatomy

They have no eyes, but instead rely on a bundle of nerves that receive and interpret sensory data which allows it to respond to the environment. Each worm contains both male and female reproductive organs but cannot self-fertlize and still require a partnership to reproduce. They have a mouth, five hearts, and a very basic digestive system that includes (among other things) a crop, a gizzard, and intestine.

They're Not Nightcrawlers

While the common earthworm, Lumbricus terrestris or night crawler as it is commonly called, has a similar anatomy the difference is in what they digest. Red wrigglers prefer decaying organic matter – like your food waste – whereas the night crawler prefers soil, roots, and some dry plant matter. This makes the red wriggler far more qualified for the job of converting food waste quickly.

Diet & Habitat

Red Wrigglers eat about half their weight in food per day. If you have 500 worms, which equates to about ½ a pound of worms, they’ll eat ¼ pound of food per day. Let’s take a look at exactly what makes up their diet:

The first category is Nitrogen which includes all of your food scraps, coffee grounds, tea bags, and manure. The second category is carbon matter which includes paper and cardboard – like junk mail and toilet paper rolls, and dried plant matter like leaves, hay, or straw. The smaller the materials the more quickly they’ll turn into castings so chop or shred as needed. Really dry materials like paper and cardboard can be soaked in water before being added which will help them break down faster as well. Beware that they cannot process dairy, meats, oils, onion, citrus, or garlic.

It’s important to remember that the food and habitat are one in the same when it comes to vermicomposting. Because of this, it’s important to maintain a balance between carbon and nitrogen. Carbon is a “slow food” and Nitrogen is a “fast food”. Ideally the bin would have about two-thirds carbon matter and one-third nitrogen.

Eggshells are a great mineral resource and offer a source of grit which is what allows their gizzard to function correctly. Ideally the eggshells would be pulvarized so the worms could make use of it quickly. Other grit and mineral sources include crushed oyster shell, garden soil, or a small amount of natural sand.

Because worms breathe and sense through their skin they require a moist environment to keep the dermis in good working order. You should be able to pick up a handful of material and feel a generous amount of moisture without it puddling or pouring out of your hands. Rain or well water is best; avoid any kind of chlorinated water.

Worms thrive between 55 and 80 degrees Fahrenheit. Anything above or below this will cause severe distress and possibly death. In the summer keep the bin shaded, in the winter keep it sheltered – either indoors or underground. As the weather gets colder or hotter the amount they consume and reproduce will decline.

The Bin

side of worm bin container decorated with worm drawings

In addition to food, grit, and water, the worm bin needs to provide a few basic things:

  1. Darkness – light is stressful and if worms are stressed they aren’t eating or reproducing.
  2. Air flow
  3. Drainage – excess moisture must be allowed to escape and not left standing.
  4. Protection from extreme temperatures.

You can purchase numerous different kinds of worm bins, ranging anywhere in price from $50 to $500. We’re going to look at a couple of different ways to make your own for next to nothing.

The first option is a two-bin system that is easy to move around, fits well in a small environment, and costs around $15 to make.

diagram of two bin nesting design

This design requires two 5-gallon plastic totes and one lid, an electric drill, and a 1/16” drill bit. Drill on a surface you can easily sweep up and dispose of the plastic debris created when drilling the holes.

Place the lid on one of the bins and drill a grid of holes about 3” apart all along the top of the lid.

Next, remove the lid from the first bin and drill two rows of holes along the top perimeter of the bin. Flip it over and drill a grid of holes about 3” apart all along the bottom of the bin, including the edges where the surface is slightly lower.

On the second bin drill two rows of holes all along the top perimeter, just as you did the first bin. If you find you need more air flow in your bin you can come back and add more holes to the perimeter of both bins and to the lid. Do not drill holes in the bottom of this bin.

Slide the first bin into the second. The holes all along the bottom allow excess water to fall into the bin beneath. This bin holds the “leachate” which can be added to flower beds or pots, or standard compost piles. The top bin is the primary habitat for the worms where you’ll add leaves, paper, and other carbon material, the worms, and food waste. As the carbon and nitrogen are consumed the bin will fill with castings, the biologically rich material that makes vermicomposting so special.

top view of worm bin inside of worm bin

The second option uses a flow-through design system that makes harvesting the castings slightly simpler.

three bin worm bin diagram

You can use any kind of nesting containers you can find. In this example I used plastic cat litter bins. You can also use 5 gallon buckets that can be purchased or sometimes found at bakeries that purchase bulk icing or batter. Do not use any buckets that contained toxic chemicals, paint, glue, etc.

You need three buckets and one lid, an electric drill, a 1/16” and a 3/8” drill bit. Place one lid on one bin and using the 1/16” drill bit, drill ventilation holes all along the surface of the lid, 2 or 3” apart. Remove the lid. In the bin drill the two rows of the same sized holes all along the perimeter above where the bins sit into one another. Turn the bin over and drill at least 8 3/8” migration holes on the bottom surface. Repeat this same drilling pattern for ventilation and migration holes on a second bucket. For the last bucket only drill the 1/16” ventilation holes, not any bottom holes. Stack the bins from bottom to top in this order:

  1. bucket with no bottom holes
  2. bucket with bottom holes
  3. bucket with bottom holes
  4. lid.

The top bin is where you’re going to add carbon material, worms, and food scraps. Once this bin gets about ½ full of castings swap this bin with the one in the center. Add carbon material and food scraps to the top bin just as you did before. As the worms migrate up to find the new food they’ll leave the middle bin behind and you can then harvest the castings from it with the majority of worms in the top bin. The bottom bin collects leachate, or excess moisture from the digestion process, and needs to be emptied every few weeks as to not swamp the worms in the second bin.

photo of three bin design from cat litter bins

Both of these bin designs have a max worm capacity of about 500 or ½ lb of worms. Because they reproduce quite quickly starting with 250, or ¼ lb of worms gives them space to grow into. In ideal conditions each worm will lay an average of 2 cocoons per week with about 4-6 worms per cocoon. When your bin gets crowded you can make a second bin to move half of them to or share them someone who would like to start a bin of their own. Do not release them into your yard, garden, or any wild area where they’ll compete with resources native organisms rely on.

close up of worm cocoon in early stage
Cocoons transition from yellow to red as they progress to hatching. One cocoon will contain 4-6 worms.

Harvesting castings

Harvesting is quite simple and can be done whenever you feel there’s an adequate amount to do so. If you’re using the two-bin design feed your worms any food waste on one side of the bin. They’ll congregate in this area and you can harvest from the opposite side. In the flow-through system simply swap the buckets and wait until they’ve had time to migrate to the upper bin before harvesting the center bin. When you remove castings from either system lay it out on a plastic bag, tarp, or other non-porous surface. Gently remove any worms still in the castings and place them back in the bin. The castings will be sticky and wet. You can use them right away or you can store them in a gallon zip-lock or other sealed container for future use. If storing allow them to dry slightly before doing so.

You can use castings directly around plants, sprinkled on garden beds, or soak in water and apply as a foliar spray or drench. If soaking you can add about ½ cup of castings to 1 gallon of non-chlorinated water. Stir and let sit anywhere between 30 minutes and 24 hours before applying to the garden. This method allows you to distribute the benefits of the castings further than direct application and is useful if your yield is smaller than desired.

Troubleshooting

For the most part composting worms are very easy to keep and maintain, but there are some challenges you may run into and I hope to leave you equipped to evaluate and respond accordingly.

First, they are a living creature and like all living creatures there are some key observations that can be made about the state of their health.

If your worms are not eating, seem lethargic, or are attempting to crawl out of the bin in high numbers you need to evaluate the moisture level, the temperature of the environment, and the balance between nitrogen and carbon material in the bin. Too much nitrogen and the bin will become too acidic for the worms to live. Too little and they won’t have enough to eat. Too much water will make for an anaerobic and suffocating environment . Too little water and they’ll be unable to breathe or respond to their environment. Check on them at least every other day as you become familiar with your bin’s general mode of operation. If going on vacation it would be wise to prep the bin ahead of time and have someone check in at least once every few days.

Because a lot of nature really loves decaying organic matter from time to time you’ll have other creatures find their way into the bin. Most are harmless, but some things to look out for include:

Lastly if your bin smells terrible it needs to be rebalanced. Too much water will create anaerobic conditions that lead to foul odor. Too much nitrogen and not enough carbon will also lead to a foul odor and inhospitable environment for the worms. Most times the solution is to add more carbon to either soak up excess moisture or balance out too much food waste.

Lastly, know that the routine care required to maintain a worm bin is quite minimal. Every few days check moisture levels, feed them soaked carbon (paper) material and food waste, empty any leachate, and once every few months give them some grit and harvest the castings.

Additional resources