Friday, April 18, 2014

Vermicomposting Basics

A few weeks ago I taught a class on vermicomposting for a local group. This post is a modified version of the handout I created and used during the class.

What is Vermicomposting?

“Vermi” in latin means “worm” and compost is the process of turning organic waste into soil. Vermicomposting is simply making soil with worms. Vermicompost is the end product and is a very nutrient-rich, organic compost full of microbes. It is also known as worm castings or worm poop.

Why do it?

There are many reasons to compost with worms.

  1. Compost indoors. It’s cold in the winter
  2. Local, efficient recycling of organic matter.
  3. Divert food waste and paper products from the landfill. It is estimated that 1/3 of all waste is from food.

What do I need?


    1. A bin
    2. Worms – red wigglers aka Eisenia fetida
    3. Worm food and bedding

Nice to haves:

    1. Knife or scissors to cut scraps
    2. A shredder for cutting bedding material (cardboard and paper
    3. Small rake/scooper
    4. Container to collect scraps

Worm Needs

Worms have similar needs to humans. They need oxygen, shelter, food, and water. They need a moist, temperate environment with temperatures between 40 and 80F with the sweet spot 65-70F. They also like it dark. They need good airflow to breathe as they breathe through their skin. I keep my worms in the kitchen year-round for easy access.

What to use for bedding?

Shredded cardboard is great bedding. It is absorbent and it doesn’t mat down when wet like normal office paper. When mixed with cardboard, newspaper and paper work well. Sawdust, hay, and dried leaves can also be used. They cannot eat plastic and glossy paper, so those should be avoided.

What to feed?

Worms will eat most any kitchen scraps, but they seem to like fruit the most. Other good options are veggies, coffee grounds, tea bags, plate scrapings, egg shells, bread, pasta, and peels. Worms don’t like spicy food like onions and garlic, so feed them in small amounts. Large amounts of citrus should also be avoided. Greasy foods including meat, dairy, bones, and fish should be avoided. Make sure to remove sticky labels, rubber bands, plastic, tea bag staples, and other inorganic material before adding scraps to the bin.

Worm Reproduction?

Worms are hermaphrodites, meaning they have both gender’s sex organs. Two adult worms are needed to make fertilized cocoons. An adult worm can lay about 2-3 cocoons per week. The cocoons hatch in 18-28 days and there are between 2-4 worms per cocoon. It will take about 28 days for a worm to reach maturity after hatching.

How to feed?

Smaller scraps will be processed faster than large pieces by the worm bin. Scraps can be torn or cut before being put into the bin. Put small amounts of food and rotate around the bin without feeding in the same place twice. When feeding, add some fresh bedding to help absorb moisture from the scraps and help keep aeration. Feed regularly, but not too often. Feeding too often could create adverse conditions for the worms by generating extra heat or gases harmful to the worms. Feeding two to three times a week is recommended. Worms can eat about half their weight in food each day, so one pound of worms can eat ½ pound of food a day.

How to harvest worm castings?

Castings are ready to harvest when the food scraps and bedding have been fully processed and are not recognizable. This can take between one and six months depending on the strength of the bin. There are several ways to harvest. One simple method is to dump the bin and sort the worms and finished compost by hand. Another way is to shine a bright light on a finished tray. The worms will migrate away from the light since they do not like light. A third way is to add a pile of fruit into a mesh bag. Most of the worms will move into the fruit inside the bag and can be easily removed from the compost.

How to use vermicompost?

Use it like compost from an outdoor bin. It can be dug in lightly to the top soil of a garden or added to the soil of house plants. Vermicompost is fantastic for starting seedlings too.

Some Worm Myths

  1. It will smell bad! A properly functioning bin smells of fresh soil. It does not stink.
  2. Worms and bugs will invade and take over! In a properly functioning bin, the worms will not want to leave.
  3. Too much time! It takes less than 10 minutes a week to feed and maintain a small bin.
  4. It’s too expensive! It can be as cheap as you want it to be. You only need worms and a bin. Worms are about $20-30/pound and plastic bin can be had for $5.
  5. Worms are gross! This can be tough to overcome. Worms are part of the natural world. A bin can be maintained without ever touching a worm.

Worm Resources

  1. My Website: Everyday Urban Gardener
  2. Find places to get worms
  3. Book: “Worms Eat My Garbage” by Mary Appelhof
  4. Vermicomposting fanatic
  5. Vermicomposting videos
  6. Worm Factory 360
  7. A Vermicomposting Guide for Teachers:
  8. Vermicomposting (New Mexico State University):
  9. Worm Composting Basics (Cornell University):
  10. Small-Scale Vermicomposting (University of Hawaii):
  11. How to Vermicompost at Home or Work:
  12. Vermicomposting FAQs:
  14. Composting with Redworms:
  15. Wikipedia – Vermicompost:


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