Here’s What You Can Do If Your Compost Stinks

Last updated on October 23rd, 2023 at 08:29 pm

A compost heap in the garden has many advantages: You produce humus with little effort, that is, 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.

Compost stinks – what to do

After heavy rainfall, compost may start to stink. However, this only happens if the wrong decomposition processes are taking place inside.

Here's What You Can Do If Your Compost Stinks

If the compost pile is not aerated enough, the waste begins to rot and unpleasant odors form. This is because under anaerobic conditions (exclusion from air) bacteria form the malodorous gases ammonia and hydrogen sulfide, and the climate-damaging gas methane is also produced.

Compost Primer

The microorganisms responsible for the decomposition processes in compost need oxygen. If the compost is very wet or if you have put in large amounts of fresh lawn clippings, there is too little oxygen in the compost. However, rotting processes take place in a compost that is too wet, and when the compost begins to rot, foul odors develop.

If your compost stinks, then you can try removing the liquid, and therefore the bad odors, from the surface with a handful of lime or stone dust. Alternatively, you can add a thin layer of soil or sand to the compost. The substrate will soak up the liquid. And, of course, it helps to dig up the compost and aerate it. You can also mix dry clippings, horn shavings, or rock dust into the waste. A well-maintained and properly layered compost pile smells like forest soil and doesn’t stink, according to the Federal Environmental Agency.

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What can be put into the compost?

To get a good, perfect humus, you should “feed” the compost pile only with harmless material.

  • Lawn clippings (preferably pre-dried)
  • Tree cuttings, preferably shredded
  • Leaves
  • leftovers from bedding and balcony plants
  • used potting soil
  • Fruit and vegetable scraps. Excluded are citrus fruits, whose peels are often heavily treated with chemicals, and banana peels for the same reason.
  • Tea leaves and coffee grounds: only in household quantities, as they contain elevated levels of zinc and copper, according to 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 cabbage hernia or fruit rot) go into the organic waste garbage can. The high temperatures in composting and fermentation plants reliably kill plant diseases, according to the Federal Environment Agency. Plants affected by powdery mildew, rust or star soot are harmless, however
  • Plants that are colonized by the boxwood borer. Dispose of these in the residual waste garbage can.
  • Weeds we want to get rid of that carry seeds – the seeds can survive composting and continue to spread. This includes giant hogweed, for example (keep your distance: this is how toxic hogweed is).
  • Cut flowers, especially those from the supermarket, are often contaminated with pesticides and are therefore only suitable to a limited extent.
  • Eggshells – they attract rats
  • Cooked food scraps, as well as bread, meat, sausage, fish, bones – also found food for rodents. All this can be put in the organic waste garbage can if the organic waste is processed in a biogas plant.
  • Wood ash (can be contaminated with heavy metals, belongs in the residual waste)
  • Leftover charcoal from the barbecue
  • Dust from the vacuum cleaner or street dirt
  • Small animal litter (hamsters, mice) and cat litter
  • Diapers
  • Paper handkerchiefs
  • Horse manure
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For rotting to go well, make sure you have a diverse mix, layer airy and provide adequate but not too much moisture. Large branches and bushes should be shredded for two reasons: Cut apart, they take up less space, and the cuts make it easier for microorganisms to decompose the wood.

As the lowest layer, which is most compacted and thus often receives too little oxygen, “bark mulch, wood chips or straw are suitable,” according to the experts at Weihenstephan-Triesdorf University of Applied Sciences.

Compost heap – in the sun or in the shade

Some gardening guides recommend creating the compost pile under a tree in the shade to prevent the compost from getting too wet. However, a cover or fleece can also serve as a cover during precipitation. A cover also helps prevent weed seeds from approaching. Location has no effect on decomposition:

As studies have shown, decomposition of waste proceeds equally well in full sun as in shady locations.

In any case, you should ensure sufficient distance to the neighboring property because of the formation of odors and possibly occurring pests such as flies. Annoying flies are kept away if vegetables and fruit residues are covered with soil.

How long to compost

Experts advise filling the compost pile for six months and then letting it rot for another six months without adding more material:

By then, most of the components have decomposed well – this can be recognized by the fact that the fresh humus smells like forest soil. Now it can be used in the garden. One shovel per square meter should be worked in shallowly each year.

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  • James Jones

    Meet James Jones, a passionate gardening writer whose words bloom with the wisdom of an experienced horticulturist. With a deep-rooted love for all things green, James has dedicated his life to sharing the art and science of gardening with the world. James's words have found their way into countless publications, and his gardening insights have inspired a new generation of green thumbs. His commitment to sustainability and environmental stewardship shines through in every article he crafts.

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