How-To GuidesSeries: Indoor Composting

Composting at home – Vermicompost (Part 2)

In vermicomposting, a symbiosis of earthworms and microorganisms is used to transform organic matter into nutrient-dense vermicompost. In this article I explain how this works and how to run a vermicomposting system.

Vermicomposting (worm composting)

This is the second article of my mini-series on composting at home – in the first article we took a look at the general considerations of composting indoors. Now we will have a closer look at vermicomposting.

In vermicomposting (aka worm composting), specific earthworms are used to decompose organic matter. Some popular varieties are redworms (Eisenia foetida), european nightcrawlers (Dendrobena veneta) and wigglers (Lumbricus rubellus). These varieties have a few things in common:

  • they are specialised in handling a large amount of organic matter,
  • they multiply quickly and
  • they thrive in a temperature around 20° C (room temperature).

Because of these characterics they are our ideal buddies for composting (indoors).

How does vermicomposting work?

In cooperation with a variety of microorganisms (bacteria, fungi, enchytraeids [aka white worms] and several unicellular organisms), the earthworms transform organic matter into worm compost: a compost with a high nutrient-density that is directly available to plants.

Operating a vermicompost is really quite easy and as long as you ensure that some basic conditions are met, the amount of earthworms in your compost will largely exceed the natural state (in your garden).

The most important conditions are:

  1. A working temperature of around 20° C (that you usually have in your kitchen);
  2. Sufficient moisture, to keep the earthworms and co. happy (that your common kitchen scraps will supply);
  3. The right type of food (see below);
  4. An alkaline pH of at least 6,5 (which largely results from the right type of food).

Depending on the size of your system, how many worms you have and how much you feed them, you can harvest every 2-4 months. By the way, your worm population will double every three months!

What can I feed my worms?

You can feed your worms most of your kitchen scraps, including:

Fruit scraps, tea bags, fruit peels, leaves, newspaper (not glossy paper), cardboard, egg shells, coffee grounds, vegetable scraps and bioplastic.

However, you should avoid feeding your worms citrus fruits, animal products and chemicals, in particular:

Bones, any chemicals (pesticide-, fungicide-, herbicide-contaminated scraps), dairy products, cheese, any citrus fruits, meat, glossy paper, lots of cooked, marinated and salted foods.

Also, the smaller your kitchen scraps, the easier it is for the microorganisms and worms to get to work, so make sure to cut bigger scraps into smaller pieces – the smaller the pieces the quicker it will decompose.

In addition to kitchen scraps, newsprint and cardboard (no high gloss) are especially important and should make up 20% of your daily feed. Worms need the contained fibres.

The vermicomposting system

While there are huge, industrial vermicomposting facilities and medium size systems for outdoor use, we will have a look at two smaller systems that are suitable for indoor use: the worm-box and the clay tower.

Regardless of the design, most systems consist of several chambers that allow you to easily harvest finished compost without disturbing your worms – once all material has been transformed, the worms move on to the next chamber.

You pile up your kitchen scraps to one chamber and the worms get to work. Once one chamber is full you move on to the next one – the worms will slowly follow to the next chamber. Once all organic matter has been broken down, all worms (or almost all worms) should have moved on to the next chamber and you can harvest.

The worm-box

Worm box vermicompost systemThe worm-box is a simple and popular system that you can easily and cheaply build yourself. There is an endless variety of different designs, all of which are usually built from untreated wood and most of which consist of the following elements:

  1. A lid on top, that allows you to easily add the new feed (your kitchen scraps)
  2. Two or three chambers, either next to each other or on top of each other
  3. A hemp mat to cover the topmost layer of feed (keeping it moist)
  4. A basin at the bottom to catch any excess liquid (aka compost water or “worm tea”)
  5. A tap attached to the basin to drain worm tea

I will write a detailed post on how-to build your own worm-box in one of the next parts of this mini-series. If you want to skip the DIY action and purchase a worm-box, there are plenty of vendors out there – if you live in the EU I can recommend

Clay Vermicompost SystemThe clay tower

The vermicomposting clay tower is a very aesthetic alternative to the worm-box, that essentially works like the worm box – except that it is made of  breathable clay. This means that excess water can evaporate from the waste, which preserves nutrients that might otherwise be washed out. Of course the aesthetics of a clay tower vermicompost are also a good argument in favor of this system.

If you’re a talented potter you can probably build your own clay tower vermicompost (I have yet to try, I promise I’ll share a how-to once I have [and if I succeed]). Otherwise you can purchase one at (EU shipping only, and this is the only vendor I know).

A word on maintenance

Overall, a vermicomposting system requires relatively little maintenance. Nevertheless, you should regularly check on your worms and make sure the basic conditions for your worms’ wellbeing are met.

Observe and interact

A vermicompost is an ecosystem constituting countless processes and complex interdependencies. Even worm researchers are still unable to answer many questions (like how exactly worms communicate with each other or why millions of springtails appear on one day and disappear on the next).

So, if an unexplained phenomenon occurs in your vermicompost, a good approach is to react in the permaculture spirit and observe it first before reacting hastily. Nevertheless there two things you can easily keep an eye on: moisture and acidity.


You can check the moisture by taking a “fist sample”: take a handful of material from your compost (make sure to sort out worms) and press it together in your fist – some moisture should run out between your fingers. If streams of water run out between your fingers, the material is too wet. The solution: mix in dry cardboard cuttings, leave the lid open during the day and temporarily feed less. If you feel no moisture, it is too dry. The solution: moisten your compost regularly (with a spray flask) or sprinkle water some water with wet hands.


An indicator for acidity (a low pH) is an increased occurrence of enchytres (small white worms). If you have more enchytres than worms, you need to actively increase the pH – you can do this by adding garden lime to your worm compost.

To always keep the pH value in the optimal (neutral) range and to supply your worms with sufficient mineral nutrients, regularly adding garden lime to your vermicompost is a good idea. Ideally you sprinkle a large spoon or two into your compost every 3-4 weeks.

Alternatively, eggshells also contain lime and necessary minerals, but make sure to finely grind them before adding them to your compost – crumbling by hand is not enough unfortunately.

Pro’s and Con’s of vermicomposting

Finally, I have summarised the pros and cons of vermicomposting to give you an overview.

Pros of vermicomposting

  • Easy to operate
  • Essentially odorless
  • Takes large amounts of kitchen scraps
  • Works continuously
  • Highly nutritious compost
  • Pets that you can keep in your kitchen

Cons of vermicomposting

  • Cannot take all of your kitchen scraps
  • It takes relatively long until you can first harvest (2-4 months)

In the next article of this mini series on composting at home, we will take a closer look at bokashi composting.

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