Worm box: compost on the balcony and terrace

Busy helpers in the box! Organic waste from the kitchen is converted into nutrient-rich fertilizer in a worm box. Read everything about worm care and what you should consider when setting up a worm box.

Composting is not only for homeowners with large gardens. Apartment owners can also use their kitchen waste and transform the help of compost worms (Eisenia foetida) into nutrient-rich, loose worm humus, which can be used, for example, to improve flower pots – with the help of a so-called worm box. There, the worms convert more than half of their body weight every day.

A 60 x 40 x 40 cm box, which is divided by a permeable wall, is sufficient as a container. The chambers are filled alternately and the worms switch from one half to the other when they need fresh food. You can buy worm boxes ready-made or easily build them yourself. An air-permeable lid and a collecting pan for the rotting liquid (good as fertilizer) are important. Composting with worms in the “Can-o-Worms” is very clean and convenient: New trays with fresh compost are gradually placed on a collecting container. The worm humus collects at the bottom.

Anyone who thinks that a wormbox stinks is wrong. Because in contrast to organic waste bin and composter, the worm box does not emit an unpleasant odor. Rather, the smell can be compared to that of a forest floor. The reason for this are the worms. Bad odors usually arise when moist organic waste rots away in the absence of air. In the worm box, however, the rotting process takes place under aerobic conditions. The loose waste is converted by compost worms and various microorganisms – without any stink. This fact makes the worm box the ideal compost variant for balconies and patios.

Why go to the expense of a worm box?

One advantage is that it can reduce household waste. On the other hand, extremely nutrient-rich humus and liquid fertilizer are created with a worm box. The conversion to “worm humus” takes about three to nine months – and is therefore much faster than a conventional composter.

This is how the compost worms survive

In order for everything to run smoothly, temperature, humidity and food supply have to be right. The compost worms used in the worm box are slightly smaller than earthworms and usually live in the top layer of the earth – where there is fresh organic material. So that the worms can breathe through their skin, it must always be moist. If the substrate in the worm box is too dry, you should moisten it with an atomizer. However, an environment that is too wet is not good either, as this reduces ventilation. This creates anaerobic conditions and rot can spread.

Compost worms usually thrive at 15-25 degrees Celsius. An optimal location for the worm box is the hallway. But a heated cellar can also fit. Important: On the balcony, the worm box must be protected from cold temperatures in winter and from direct sunlight in summer.

Feeding compost worms – that’s how it works

The worms are fed a mixture of around 75 percent shredded fruit and vegetable waste, coffee grounds, tea bags and 25 percent moist paper, cardboard and egg boxes. This creates the ideal mixture of carbon and nitrogen-containing matter for you. Once a week you should feed them a special mineral mix. This ensures a stable pH value (five to seven) and supplies the worms with minerals and trace elements. In addition, the liquid created in the worm box should be drained every one to two weeks. The so-called “worm tea” can then be stored in open containers and added to the watering water as a liquid fertilizer in a ratio of 1:10.

Worm box: what is allowed in and what is not?


  • Untreated vegetable and fruit residues
  • tea bags (without clips and paper label and string)
  • Coffee grounds (maximum one third of the daily ration)
  • egg shells (washed and crushed)
  • Newsprint, cardboard (no color, no high gloss)


  • Strong smelling: onion peels, garlic, citrus fruits
  • Dairy products, cheese, leftover food, meat, bones
  • the peels of processed fruits and vegetables (chemicals)
  • animal feces, cat litter

Worm box: harvest worm humus

Four to six months after the worm box has been set up, the so-called worm humus can be harvested for the first time. The humus collected at the bottom of the worm box should then have a fine crumbly consistency and be black and shiny in color. You can simply sieve out the coarse pieces and put them back in the box. The worm humus serves as a highly effective fertilizer and can be mixed spoon by spoon under the soil of potted plants or – mixed with soil in a ratio of 10 to 20 percent – used for gardening.

Recent Posts