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Do you have a lot of leaves and shrubs in your garden? Then create a compost. We have a list of everything to belong on the compost and tips on what to do if it stinks.

Status: 16.09.2020

A compost heap in the garden has many advantages: You can produce humus with little effort, i.e. your own fertilizer with which the soil in the garden can be improved. Mixed with garden soil and sand, this can also be used as potting soil.

You also save elsewhere: if you consistently compost all vegetable waste from the household, you can reduce household waste by up to a third, according to a study by the Weihenstephan-Triesdorf University of Applied Sciences. According to the Federal Environment Agency, composting is "the oldest and easiest recycling process in the world".

After heavy rainfall, the compost may start to stink. However, this only happens when the wrong degradation processes take place inside.

"If the compost heap is not ventilated enough, the waste will start to rot and unpleasant smells will develop. Under anaerobic conditions (exclusion of air), bacteria form the foul-smelling gases ammonia and hydrogen sulfide, and methane, which is harmful to the climate, is also produced."

Compost primer, Federal Environment Agency

The microorganisms that are responsible for the rotting processes in the compost need oxygen. If the compost is very moist or if you have filled in large quantities of fresh lawn clippings, there is not enough oxygen in the compost. However, if the compost is too wet, putrefaction processes take place and if the compost starts to rot, then bad smells arise.

If your compost stinks, you can try to remove the liquid and with it the bad smells on the surface with a handful of lime or stone flour. Alternatively, you can put a thin layer of soil or sand on top of the compost. The substrate soaks up the liquid. And of course it helps to dig up and aerate the compost. You can also mix dry cuttings, horn shavings or rock flour with the waste. A well-cared for and properly layered compost heap smells of forest floor and does not stink, according to the Federal Environment Agency.

What is allowed in the compost?

In order to get a good, perfect humus, the compost heap should only be "fed" with harmless material.

  • Lawn clippings (preferably pre-dried)
  • Tree pruning, best chopped up
  • leaves
  • Remnants of bedding and balcony plants
  • used potting soil
  • Fruit and vegetable scraps. Exceptions are citrus fruits, the peel of which is often heavily treated with chemicals, and banana peel for the same reason.
  • Tea leaves and coffee grounds: only in normal household quantities, as they contain high levels of zinc and copper, according to the Weihenstephan-Triesdorf University of Applied Sciences.
  • Sawdust (from untreated wood)
  • Wood chippings (from untreated wood)

What is not allowed in the compost?

  • Plant residues with diseases, for example branches with fungal infestation (such as carboniferous hernias or fruit rot) are put in the organic waste bin. The high temperatures in composting and fermentation plants reliably kill plant diseases, according to the Federal Environment Agency. On the other hand, plants that are affected by powdery mildew, rust or sooty are harmless
  • Plants colonized by the box tree moth. Dispose of these in the residual waste bin.
  • Weeds that we want to get rid of and that bear seeds - the seeds can survive composting and spread further
  • Cut flowers, especially those from the supermarket, are often contaminated with pesticides and are therefore only suitable to a limited extent
  • Egg shells - they attract rats
  • Cooked leftovers, as well as bread, meat, sausage, fish, bones and bones - also found food for rodents. All of this can be put in the organic waste bin if the organic waste is processed in a biogas plant.
  • Wood ash (can be contaminated with heavy metals, belongs in the residual waste)
  • Leftovers from the grill
  • Dust from the vacuum cleaner or street dirt
  • Small animal litter (hamsters, mice) and cat litter
  • Diapers
  • Paper handkerchiefs
  • Horse manure

So that the rotting works well, you should pay attention to a diverse mixture, airy layers and ensure sufficient, but not too much, moisture. Large branches and bushes should be shredded for two reasons: When cut apart, they take up less space and the interfaces make it easier for the microorganisms to break down the wood.

According to the experts at Weihenstephan-Triesdorf University of Applied Sciences, "bark mulch, shredded wood or straw" are suitable as the bottom layer, which is most compacted and therefore often receives too little oxygen.

Create a compost heap - in the sun or in the shade

Some gardening guides recommend placing the compost heap under a tree in the shade to prevent the compost from getting too wet. In the event of precipitation, however, a lid or a fleece can also serve as a cover. A cover also helps against approaching weed seeds. The location has no influence on the rotting:

"As studies have shown, the rotting of waste works equally well in full sun and in the shade."

Guide to composting in the garden, Weihenstephan-Triesdorf University of Applied Sciences

In any case, you should ensure that there is sufficient distance to the neighboring property because of the formation of smells and pests such as flies that may occur. Annoying flies are kept away when vegetables and fruit residues are covered with soil.

Experts advise filling the compost heap for six months and then allowing it to rot for a further six months without adding any further material:

"Then most of the components are well decomposed - this can be recognized by the fact that the fresh humus smells of forest soil. Now it can be used in the garden. One shovel should be worked in flat per square meter every year."

Bavarian State Office for the Environment