By Helmut Schimmel
My first worm container resembled a small cold frame that was partially submerged in the ground and covered with a black sheet. It only produced modest worm humus yields. When evaluating my attempts up to that point and the experience I had collected, I decided to build a relatively stable and sufficiently large worm humus container that would take a minimal amount of effort but would also be suitable for use over the winter in outdoor conditions. I was aware that the size and design are already subject to certain important requirements to ensure successful vermicomposting.
Examples of important factors include
- the highest possible ratio of volume to exterior surface area
- prevention of cold air entering through the sides in winter and
- protection against drying in summer and against animals that might eat the compost.
Migration box according to the two-chamber principle
Used corrugated plastic sheets from a greenhouse complex seemed like a good choice for building the new housing for my underground coworkers. I set up four sheets, about one meter in height, in a circle with a radius of approximately one meter and embedded them into the ground, with two of them opposite from each other embedded in concrete. I attached the other two sheets between them to the parts of the first two sheets that they overlapped using screws in a way that allows them to be removed, which is important for removing the compost.
I excavated the circle of soil within the container to a depth of about twenty centimeters. Then I lined it with finely-meshed chicken wire (to keep out moles), which I embedded in concrete along with the stationary corrugated plastic sheets at the sides. I stuck a strong wooden stake directly in the middle of the circular area with a round wooden board as a cover on top. It serves as a support for covering material to protect against rain, direct sunshine, frost, cold, and snow. I call the container a “worm silo” rather than a “worm compost pile.” It works according to the two-chamber principle, with the exception that the border between the “chambers” does not physically exist.
I decided against a container with two separate chambers, which you can read about in all the publications on the topic of “earthworm migration boxes.” Building a migration box of this type requires significant expenses. An interior partition is made out of perforated bricks, and the ground is also covered with them. It must be possible for worms to travel through the wall, so it is usually made up of hollow bricks that are laid such that worms can crawl through them. From my own experience, I can say that I do not need any such partition.
The finished worm humus is made up of solid, cohesive crumbs of soil that form a stable layer. Removing the outer sheet from the worm silo allows me to easily remove the finished humus while the other half, with the worms, remains in place. Why would I need an additional partition?
Building these internal partitions is usually expensive and leads to “traffic” (in this case, worm traffic) being impeded. Earthworms love freedom and reject confinement. I guarantee my brandlings “freedom of movement” between east and west. As “nightcrawlers,” they make it out of even enclosed spaces and are present in the surrounding areas if there is sufficient moisture, and not just in the summer. Although my container functions without an internal partition, it does rely on the same principle by steering activity in the worm silo in a certain direction, i.e. luring the worms from one side to the other. A pitchfork can be employed if needed. A few weeks before it is time to collect and remove the finished worm humus from one of the sides, the remaining worms are moved to the other side along with the upper layer of food. The side that is going to be cleared out is kept increasingly dry (pre-drying the worm humus), which causes the worms to migrate to the nearby fresh food on their own. When I remove the humified soil, I orient myself by the markings on the side. It couldn’t be simpler.
Preparing the final product
I think the size of my container is well suited to my 350 square meter community garden plot. The surface of my worm silo takes up at least three and a half square meters of ground area. Every year, I empty half of it.
I use part of the mature humus immediately, without sifting it, to improve the soil quality in my garden. I spread the other half over a tarp and let it dry in the air until it can be sifted. The Optimus Society strongly stresses this sifting process as it produces an especially pure and high-quality end product. They recommend using a particularly fine sieve (two millimeters).
Going to all this effort makes the preparation laborious and expensive. The dried and sifted worm humus has a long shelf life and can be stored without any issues.
In total, I produce more than 1.5 cubic meters (about one metric ton in weight) of worm humus per year. This is enough to make me completely self-sufficient. The next year, the vermicompost in the second chamber is ready for use. As soon as one half has been completely emptied out, it is immediately replaced with new seeded material. Then the worms can go back to feeding from both sides.
Next up: Chapter 8: Worm Keeping in Winter
About the Author of Compost Revolution
Helmut Schimmel is a longtime authority on the care and reproduction of earthworms and the production of valuable worm humus. His coworkers in this venture belong to Eisenia fetida—earthworms which are indispensable in the humus economy. Expert gardener and horticulturist Helmut Schimmel draws from his great wealth of knowledge acquired over decades of study and practice to yield this single, definitive book on the practice.