Since 2015, organic waste in Germany must be collected separately and disposed of in organic waste bins or at recycling centers. This means that all garden and kitchen waste generated in private households must be handed over to the public waste disposal authority. However, waste that garden owners compost themselves on their property is exempt from this rule.

Humus and compost

The first layer of soil, approximately 40 cm thick, is called humus. It is created through gardening and the regular addition of dead organic matter (e.g., compost). This layer contains all the nutrients that are important for plants, such as nitrogen, phosphorus, potassium, and others. It is also home to living soil organisms such as fungi, bacteria, algae, worms, insects, and other microorganisms. They contribute to the formation of humus by decomposing organic material, aerating the soil, and processing the necessary nutrients.

A constant pH value in the soil is also important for maintaining good soil quality and promoting the nutrient cycle. Compost fertilization prevents lime from being washed out and the soil from becoming acidic. Leaching causes nutrients to enter the groundwater and ultimately leads to overfertilization of water bodies.

How is compost produced and which materials are suitable for the garden?

Organic material is decomposed by the above-mentioned soil organisms. The speed of decomposition depends on the temperature in the soil, the moisture content of the material, the oxygen content, and the pH value. Wilted grass clippings, leaves, hedge trimmings, fruit and vegetable scraps, coffee and tea filters, and eggshells are very suitable as source materials. Moderately suitable are tropical fruit peels, paper and cardboard, plant-based small animal bedding, and wood ash from untreated wood.

On the other hand, granulated animal litter, diseased plant parts, or plants that have been treated with herbicides are not suitable. Under no circumstances should meat scraps, food scraps, or bones be added to the compost.

Creating a compost heap

Choose a shady, wind-protected location with well-drained soil. You can create a pile that should not exceed 1.5 m in height and 2 m in width. In small gardens, a composter—a frame made of slats, which you can easily purchase at a hardware store—is suitable. Alternatives include plastic composters or thermal and rapid composters with targeted ventilation and heat insulation. If you don't have a garden, you don't have to miss out on composting! So-called worm bins or worm farms allow you to compost in your city apartment. You can find more information on this in the list of links below.

How do you compost properly?

Create the best living conditions for the microorganisms in your source material to ensure successful composting. When setting up the compost, make sure it is sufficiently moistened (too much water, on the other hand, leads to rotting, which you can recognize by the unpleasant smell). The compost material must also be well aerated, as the microorganisms need oxygen. You can tell that your microorganisms are working well by the strong heating during the composting process ("rotting"). You can speed up the process by shredding the source material well and mixing woody plant parts with soft material. The more diverse the waste, the better the rotting process.

Never add large quantities of a single material, such as all the grass clippings after mowing, to your compost heap.

To start the rotting process, you can add a few shovels of finished compost or garden soil. The microorganisms contained in these will essentially inoculate the compost. Commercially available "compost accelerators" are not necessary.

For faster results, turn the compost 1–3 times a year.

When is the compost ready?

Partially decomposed compost is ready after 3–4 months and can be used for mulching or soil improvement. You can recognize mature compost by its uniform, fine crumbly structure, which is achieved after approx. 6–12 months. The smell of damp forest soil indicates that the compost is now ready for use.

When should compost be applied?

Compost should only be applied during the growing season, i.e., in spring or summer. This is because plants can only absorb nutrients during the main growing season.

Seven tips for successful composting

Composting area: Choose a shady, wind-protected, unsealed location with soil as a base so that earthworms and other microorganisms can penetrate.

Substrate: Loosen the substrate and pile coarse material approx. 10–20 cm high as the bottom layer.

Compostable materials: Sprinkle leaves and kitchen waste over the substrate. Only mix in a thin layer of wilted grass clippings to prevent rot. Always chop everything up well and mix thoroughly.

Starting compost: "Inoculate" the newly created compost with some garden soil or add compost worms.

The right climate: Since microorganisms need moisture, the compost must be kept moist. If it is too wet, the decomposition process will come to a standstill. Due to a lack of oxygen, fermentation and rot will set in instead. Therefore, always ensure good ventilation and do not use closed containers.

Turning: When you turn the compost (heap), the compost is mixed and aerated. This promotes decomposition. Sieve the finished compost and put any undecomposed material back on top.

Finished compost: Protect it from moisture and drying out with leaves or wood until you are ready to use it.

The Mainz Environmental Store currently has a mini worm station for urban gardeners to marvel at. In addition to lots of information on composting, the exhibition on organic waste bins, which runs until October 30, 2020, also shows you numerous alternatives to this.