Correct composting

Composting is the biological process of the nutrient cycle in which shredded organic waste is broken down by micro-organisms (mainly bacteria, fungi and actinomycetes, later earthworms, woodlice, nematodes, springtails and many other small creatures), releasing nutrients and forming humus in some cases.

Any amateur gardener can compost waste, provided that they are prepared to invest a little time and follow a few simple principles: Firstly, you should find a suitably shady spot in the garden where decomposition will be easy, as this is the only way to provide the micro-organisms with enough oxygen to enable them to break down and convert the waste material of their own accord. It is also important to maintain the right level of moisture (not too dry, but not too wet either. A moisture content of around 60% in the composted material is perfect). During composting, the activity of the micro-organisms can generate temperatures of up to 70 degrees.

Many different compost containers are available to buy that will mainly be of interest to owners of small gardens. These should be made from wood or plastic, not metal (corrosion). Two-chamber or multi-chamber systems are the best choice: you collect all your waste in the first container and then create your compost heap in the second container by mixing the coarser waste (e.g. shrub cuttings) with grass clippings, moist, nutrient-rich vegetable waste and dry material (e.g. leaves) and/or nutrient-poor wood chippings or by loosely layering these materials one on top of another in thin layers (do not compress, as a lack of oxygen will case the material to rot, so that it decomposes slowly and inadequately, producing a foul smell). After about three months, the half rotted compost is transferred to the next chamber, where it can reach full maturity.
“Compost accelerators” are mostly unnecessary: Mixing a couple of shovels of mature compost with newly started compost will be just as effective as a “starter culture”. It can also be beneficial to add a mixture of around 1 kg of sugar and approx. 100 g of yeast dissolved in about 10 litres of lukewarm water.

Most components will be well broken down after about a year and the resulting dark-coloured compost will typically smell like soil. Any material that has not fully rotted should be removed using a sieve, shredded again if necessary and then mixed back into the new compost.

What can and should be added to the compost (in a well-shredded state): Grass, shrub and herbaceous clippings, leaves, vegetable waste and cut flowers, coffer grounds and filters, teabags, egg boxes, egg shells, pet litter, newspaper, kitchen roll, paper hankies, wood ash, weeds, provided they have not gone to seed, couch grass provided it has fully dried out. Citrus fruit peels and banana skins rot very slowly, particularly because they are mostly treated with chemicals, but are not a problem in small quantities.

What should NOT be added to the compost: Fat and oil, leftover food of animal origin, such as meat, cheese, bones and baked goods, as this can attract unwanted guests such as rats, foxes or even raccoons, and an unpleasant smell may occur. Vacuum cleaner bags, magazines, stones, leather, plastic and composite materials such as coated fruit juice or milk cartons and metal and treated wood are also unsuitable for composting purposes.

Plants such as cucumbers, melons, pumpkins, courgettes, etc. can be planted in the semi-mature compost heap as these will thrive here and will provide a reliable indicator of the moisture levels in the compost.

The success of composting efforts also depends on the environmental conditions (periods of rain and drought, shade, etc.) and, above all, the right compost care regime. Compost prepared in this way will usually be ready within a year and will be a very good soil improver in the garden, acting as an excellent fertiliser, particularly in the vegetable garden and in raised beds.

Prof. Karl E. Schönthaler
VIKING garden expert