Why Compost Sometimes Rots Badly

Last updated on October 23rd, 2023 at 08:31 pm

The Nutrient Content – The Ratio Of Carbon (C) To Nitrogen (N) In The Compost Heap

I have not previously described this issue with nutrient content, as it is not relevant to a correct compost pile construction as I have described.

Why Compost Sometimes Rots Badly

So, if you fill your compost pile in layers with the materials you want to compost, such as lawn clippings, hedge trimmings, bedding debris, leaves, or chipped tree trimmings. Wet and dry materials should be mixed to prevent the formation of zones that are too dry or too wet, which can negatively affect or stop the rotting process. Important for success is old compost from the previous year (alternatively Terra Anima® humus soil), which is introduced in small quantities when building the compost pile.

However, anyone who has ever forgotten a pile of fresh lawn clippings knows the problem. Within a few days, the grass has turned into a stinky green pudding.

Why Is This?

Why is it that a pile of wood chips, pure straw, or sod without healthy mixing tends to rot or stink but not decompose? It’s because of the nutrient content.

In composting, the activity of the decomposing microorganisms depends on the C/N ratio, or carbon content to nitrogen content.

A high nitrogen content is found in green waste, such as turf, meadow herbs, nettles, flower clippings and other fresh garden waste.

High carbon content is found in straw and hay, wood chips and other wood and grain residues.

Microorganisms need nitrogen to decompose green material. In this process, a high nitrogen content accelerates the rotting process. The nitrogen can be seen as food for the microorganisms.

In a compost with a high carbon content and very little nitrogen, the nitrogen for rotting is quickly used up and rotting comes to a halt due to lack of food for the soil life. I wrote something here about the problems with nitrogen in agriculture.

What Is The Effect On Nutrient Content?

Compost with too much N has a strong fertilizing effect and does not meet the needs of many plants. Plants with low or medium nutrient needs become susceptible to diseases and pests, and they develop watery fruit.

A high carbon content in compost delays rotting. When it is applied to the bed, nitrogen fixation occurs, which means the decomposing microorganisms pull the needed nitrogen from the soil. This nitrogen deficiency in the soil then leads to short-term growth disorders in the plants.

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Nature solves this problem by blowing the excess nutrient into the air, namely carbon in the form of carbon dioxide and nitrogen in the form of ammonia and nitrous oxide. These gases are highly relevant to climate change.
Ammonia also offends our noses. The C/N ratio to aim for is 15:1 to 35:1, i.e. 15 to 35 parts carbon to one part nitrogen.

This Is How Long Waste Takes To Decompose

Not all waste is the same: How long various everyday products take to decompose depends on the material and the external circumstances. Here you can find an overview of the decay time of typical everyday products.

Separating and disposing of waste correctly is important for environmental protection. One of the reasons for this is that certain materials are particularly long-lived. Some waste decomposes only very slowly or does not decompose at all. In the process, some waste materials can harm ecosystems and permanently pollute nature with harmful residues.

How long waste takes to decompose depends on its composition, for one thing. But environmental conditions also play a role. On this basis, at least guideline values for the decomposition time can be determined.

By the way: Depending on the material, there are different designations for the decomposition process. Only organic waste, such as plant residues, can decompose. They are decomposed by bacteria and other microorganisms. Other materials such as glass and metal are subject to gradual decomposition by the weather. In the case of metal, expert:inside speak of corrosion.

Waste decomposition: Why exact values are difficult to determine

It is not very easy to set exact values for the decomposition time of different wastes. There are several reasons for this.

On the one hand, it is due to the fact that, especially in the case of man-made materials, the composition of the material can vary greatly. For example, not all plastic bags are the same: depending on the chemical composition, size and thickness of the bag, the decomposition time can differ by decades or even centuries. For this reason alone, it is difficult to make a generally valid statement.
In addition, outdoor conditions play a role. Depending on weather conditions, the decomposition process takes longer or shorter. Orange and banana peels, for example, decompose considerably faster in tropical climates than at Central European temperatures.
Nevertheless, a rough time window can be defined for most waste. In this overview, we present the most important types of waste and their decomposition time. We mainly follow the data of the Austrian Alpine Club and the Aktion Müllfrei.

Organic waste: They do not always decompose without complications

Why Compost Sometimes Rots Badly

Because of its natural origin, organic waste is generally regarded as unproblematic and quickly decomposable. But it’s not quite that simple: While an apple skin, for example, only needs about two weeks to decompose completely in nature, tropical fruits take much longer. As the Alpine Club writes, they only rot quickly in tropical climates. In addition, imported fruits are often treated with sprays and/or synthetic pesticides if they are not organic, according to the Augsburger Allgemeine.

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On average, therefore, the following decomposition times apply to various fruit residues:

  • Apple skin: 2 weeks
  • Banana peel: at least 6 weeks, often 1 to 2 years
  • Orange peel: 2 to 3 years

It is therefore advisable not to simply throw organic leftovers into the open air, but to dispose of them in the organic waste garbage can. You can find out more about which waste belongs in the organic waste garbage can and which doesn’t in our guide: Organic waste garbage can: What can go in – and what can’t.

Natural waste materials: paper, metal and glass

Paper consists of wood fibers and is therefore actually a natural product. In purely theoretical terms, it should therefore rot quickly in nature. In fact, however, this only applies to largely unprocessed paper. Everyday paper-based products are usually further processed and contain additional substances that ensure greater stability and longer shelf life. In the case of newsprint, for example, the printing ink contained is responsible for a much more protracted decomposition process, according to the Alpine Club. Accordingly, the decomposition times of different paper products differ:

  • Paper bag: 6 weeks
  • Cornflakes and cereal packaging: 6 weeks
  • Newsprint: 1 to 3 years
  • Paper handkerchief: 3 weeks to 5 years

Because paper is easy to recycle, you should make sure to dispose of it in the waste paper garbage can. This way, it does not simply decompose, but can be further processed. You can read more about this here: Paper recycling: How it works and what becomes of the paper.

Metals are also naturally occurring raw materials. Unlike organic waste or paper, however, they do not rot but corrode due to environmental influences. This usually takes a long time. Exactly how long depends once again on the material and how it is processed:

  • Sheet metal: 50 to 500 years
  • Aluminum: 10 to 100 years
  • Aluminum foil: 200 to 400 years

Many cans made of sheet metal or aluminum are easily recyclable. However, can recycling is also criticized in terms of sustainability. You can find more detailed information on the topic in our article Can recycling: How sustainable is it?

Glass is made of quartz sand and takes by far the longest of all natural materials to decompose. Depending on environmental conditions, a glass bottle can last between 400 and one million years, according to Augsburger Allgemeine. However, glass is also a recyclable raw material; read more about this in the article Disposing of used glass properly.

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Problematic plastics: plastic, nylon, polystyrene

Although plastic also gradually decomposes, it is not completely degradable: According to the Federal Environment Agency, plastic is “biologically inert”. This means that plastic decomposes into smaller and smaller particles over time, but they never fully decompose. In this way, plastic waste pollutes the environment with secondary microplastics.

Even alternatives such as bioplastics are not without problems: although they are biodegradable in principle, they usually take a long time to do so. Their eco-balance is also questionable due to the manufacturing conditions, and recycling is difficult in practice. You can read more about this topic in this article: Biodegradable, compostable, bio-based: Here’s the difference.

Even for this incomplete degradation process, plastic and other plastics take a very long time. In the case of Styrofoam, the maximum decomposition period is even considered unmeasurable: if Styrofoam waste is not exposed to the elements (i.e. wind and water, for example), it is “virtually eternally durable,”

The figures from the Alpine Club and other sources therefore only refer to the period of time during which plastic products “dissolve”, so to speak, and are apparently no longer perceptible. Residues still remain in nature even after these long periods of time:

  • Plastic bags: 100 to 500 years
  • Plastic bottle: 450 to 5,000 years
  • Tetrapack: 50 to 100 years
  • Nylon fibers: 60 years
  • Styrofoam: 6,000 years and more

Especially with plastics, proper disposal is therefore very important. You can find out more about this in our articles “Yellow garbage can: What can go in and what can’t” and “Disposing of styrofoam: What you need to watch out for.

You can also find out more about microplastics at Utopia – for example, we give you tips on what you can do against microplastics and introduce you to good alternatives to products with microplastics.


  • 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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