Composting vs. Rotting: Differences Explained

If you’re new to the composting world, you probably think composting looks a lot like rotting. However, these are two different processes. So, what’s the difference? 

Composting can be seen as a form of rotting, but because the materials are primarily plant-based, the compost doesn’t have the same qualities often seen in rotting foods. Things like heavy odor and maggots don’t typically exist in compost, but they do with rotting.

The rest of this article will discuss what composting is, and what makes it different from rotting. Let’s get started!

Key Differences Between Composting and Rotting

Although these two are often synonymous in people’s minds, there are differences between them.

While composting can be seen as a form of rotting, it’s more aptly described as simply breaking down. Rotting indicates that something is decomposing — usually with parasites, maggots, and worms involved.

Here’s a table to give you a quick overview of the differences between composting and rotting:

Types of Materials
  • Plant-based materials.
  • Peels, vegetables, etc.
  • Specific materials to encourage compost.
  • Any material – meat, eggs, carcasses, plant materials, etc.
Decomposition Process
  • Aerobic decomposition.
  • Uses naturally occurring microorganisms to break down food.
  • Typically anaerobic decomposition.
  • Uses worms, parasites, maggots, etc., to digest some of the materials.
Oxygen Content
  • High oxygen content due to the organisms used.
  • Minimal oxygen content.

As you can see, composting can be a type of rotting because both are a breaking down of materials, but it’s difficult to define it as such because there are quite a few differences between the two. 

The Types of Materials Used

One of the biggest differences between composting and rotting is the type of material that is contributed to the composting pile. Compost piles tend to have specific materials that produce aerobic decomposition, filling the soil with oxygen and various microorganisms that assist in the decomposition process. 

Concerning rotting, there aren’t specific materials that are used. Any living organism that has died will rot. This process happens relatively quickly once life has ceased in the organism. Other organisms, such as maggots, worms, various parasites, and more, contribute to decomposition. 

Composting, on the other hand, tends to require constant vigilance in using the right materials. Most people who compost are even hesitant to put things like rotting fruits in their compost pile. This is because once the food begins to rot, it often develops illnesses such as E.Coli, Salmonella, and Listeria. It can also develop other unwanted organisms. 

When the material is put in the compost pile while relatively fresh, it’s affected by different microorganisms. Before the ones that cause the food to rot can attack, the food begins an entirely different decomposition process. 

The Decomposition Process

Even though composting and rotting are types of decomposition, the way this happens looks quite different between the two. 

The main difference in the decomposition process is that composting is very controlled, whereas rotting occurs sporadically.

Compost Decomposition

Microorganisms are the key players in the composting process. The only way to compost properly is to create the perfect environment for these specific microorganisms to flourish. The best way to do this is to create an environment with: 

  • Warm temperatures
  • Nutrients
  • Moisture
  • Excess oxygen

The first stage of composting only lasts a couple of days. During this time, mesophilic microorganisms, which thrive in temperatures between 68 and 113 degrees Fahrenheit (20 and 45 degrees Celsius), begin the breaking down process. This breaking down process produces another key factor in composting — heat. The initial temperatures rise to around 104 degrees Fahrenheit (40 degrees Celsius). 

After a couple of days, the mesophilic microorganisms are replaced by their friends, thermophilic microorganisms. Thermophilic microorganisms last for anywhere from a few days up to several months. They work to break down all the organic materials into thinner and finer pieces, and the high temperatures strongly assist with this.

However, you must be very careful when handling your compost, as it can become very hot. For more information about this, be sure to take a look at my other article on managing heat in your compost pile: Can a Compost Bin Get Too Hot? Important Things To Know 

Over time, the microorganisms completely break down all the materials in the compost pile. New microorganisms emerge as new material is added, and the process continues cyclically. The result is a decomposition process that produces thousands of beneficial nutrients that can then be used to grow new plants. 

Rot Decomposition

Rotting, sometimes referred to as spoilage, is similar to compost in how the decomposition process works. They work with various microorganisms, but the rotting process is enormously sporadic and uncontrolled. 

The rotting process begins for a few different reasons. Usually, it starts when food comes in contact with mold spores or a similar decomposition agent. Once the rotting process begins, it attracts various bacteria and other microorganisms.

You’ll notice that the smell is often horrendous when food is rotting. This begins with bacterial waste, which is what produces the initial odors. The odor of the bacterial waste eventually attracts other organisms, such as flies, which breed and produce maggots. In addition, if the food is left outside, it’ll attract specific parasites and worms. 

While compost also welcomes certain types of worms (such as earthworms), the worms and parasites attracted to rotting food don’t provide the same beneficial nutrients as earthworms. 

The rotting process involves almost exclusively bad bacteria. Composting, similar to fermenting, involves a mix of good and bad bacteria. 

As food rots, it releases a mix of various gases and odors. This is usually more intense when meat, dairy, and eggs rot. Like smelling roadkill while driving, you can expect to smell something similar if you have animal products rotting nearby. What you smell heavily depends on what materials are rotting and what microorganisms have found their way into the food.

Eventually, full decomposition takes place. The food is broken down relatively quickly with both processes, but it’s broken down faster with compost. Because the rotting process is so sporadic, it can take significantly longer than compost. 

The Oxygen Content

A major difference between composting and rotting is how much oxygen each has. Composting is primarily done through an aerobic process — meaning that the microorganisms involved function in and produce additional oxygen. On the other hand, rotting is primarily an anaerobic process, meaning that the microorganisms involved function in and produce minimal oxygen. 

How much oxygen the materials have access to makes a big difference in how the decomposition happens. A higher oxygen content will produce what you typically see in compost — rapidly decomposing materials with minimal odor. You’ll also notice that more heat is produced with excess oxygen. 

A lower oxygen content, on the other hand, produces a different result. Of course, it’s not only the low oxygen content that produces an intense smell and slower decomposition. Most of this is due to the types of bacteria in the decomposing material. 

Is Composting Rotting Food a Good Idea? 

Since composting and rotting foods have quite a few similarities, you may be wondering whether or not you should compost some of your food that’s starting to rot. The answer to this question depends on what foods are rotting and what type of rotting is taking place. 

Molding food is typically fine to add to compost since mold naturally occurs on foods. On the other hand, things like spoiled lettuce shouldn’t be added to compost piles since they risk carrying other diseases. 

Mold might be gross, but it isn’t usually dangerous. Molding typically takes place when fruits and veggies aren’t harvested in time. This type of mold is completely safe to add to your compost pile. 

However, what about mold that grows when food is left in your fridge or on your counter for extended periods? 

This mold is typically green, whereas the molding that occurs when foods are harvested too late is white. This mold isn’t going to hurt anything if you place it in the compost pile, but it’s also not going to benefit your compost pile because this type of mold will die off quickly once placed in the compost pile. 

If you’re adding moldy food to your compost pile to further develop and encourage the compost to flourish, you’ll only want to add specific molds. However, if you’re adding only to get rid of it, then it really doesn’t matter how you do it. 

But what about rotting foods that aren’t moldy? 

Foods like brown and slimy lettuce shouldn’t be composted. This is because rotting greens are more likely to develop other foodborne illnesses such as Salmonella. The bacteria is usually present on the green vegetables from when you buy them at the store. They aren’t usually a threat while the food is fresh, but will become active as the greens start decomposing.

If you place things like this in your compost pile and then use it for things, it can transfer diseases and make you quite sick

Final Thoughts

Composting and rotting are primarily differentiated through the types of materials used, the decomposition process, and the oxygen content. 

While composting is sometimes considered a type of rotting, it’s a different process that requires cultivation and effort. On the other hand, rotting is typically very sporadic and requires no specific cultivation procedures.

If you found this guide helpful, I recommend my complete guide on composting with and without a bin. You’ll learn how you can manage your composting easily, harvest the perfect homemade soil conditioner, and use your compost: How to Compost With and Without a Bin (Ultimate Guide)

Alexander Picot

Alexander Picot is the principal creator of, a website dedicated to gardening tips. Inspired by his mother’s love of gardening, Alex has a passion for taking care of plants and turning backyards into feel-good places and loves to share his experience with the rest of the world.

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