3 Reasons Your Compost Heap Has Gone Cold

Having a compost heap is a great way to ensure your garden receives the best nutrients while using your kitchen waste and reducing your carbon footprint. However, while composting may seem to be an easy task, there are specific requirements for a successful compost heap, and heat is one of them. So you might be wondering why your compost heap has gone cold? 

Many things can go astray with a compost heap, causing it to go cold. However, the top three reasons for a cold compost heap are too little oxygen in the compost heap, too much water in the compost, and insufficient nitrogen-rich materials. 

Your next question might be how these factors influence a compost heap and cause it to go cold. You will also ask how you fix these problems to get your compost heap back to its ideal 150°F (66°C). This article will discuss how these factors can cause a compost heap to go cold and how to fix them to ensure your compost heap is working at its best. 

Why Does a Compost Heap Go Cold? 

If you have ever seen a perfectly healthy compost heap, you will notice that it is warm and doesn’t smell bad. However, if your compost heap is cold and smelly, it means that the bacteria in your compost heap are not working efficiently. 

A compost heap with a temperature of 150°F (66°C) is full of aerobic and anaerobic bacteria that work together to break down the materials and turn them into compost. For these bacteria to work efficiently, your compost heap needs to have enough air, sufficient water, and the correct ratio of carbon and nitrogen nutrients. 

If any of these factors are not ideal, the bacteria in your compost heap will stop working, and your compost will go cold. While the plant materials will still eventually turn into compost, this process might take as long as three years.

Apart from the compost heap feeling cold to the touch, there are other signs that the bacteria in your compost heap are not working efficiently. Here is a table with the leading causes, warnings, and solutions to fix a cold compost heap. 

Signs That A Compost Heap Has Gone ColdProblems That Cause A Compost Heap To Go ColdSolutions To Ensure A Compost Heap Regains Its HeatPrevention To Ensure A Compost Heap Doesn’t Go Cold
The plant materials in the compost heap are dense or matted.There is not enough air in the compost heap.Turn over the compost heap with a pitchfork.Turn over your compost heap using a pitchfork every two weeks.
The compost heap smells bad.There is too much water in the compost. Add dry material to the compost.Shelter the compost heap during the rainy season. 
The plant materials in the compost heap are not breaking down. The carbon-nitrogen ratio in the compost heap is not correct.Add more carbon materials to the compost heap.Ensure that the carbon-nitrogen ratio is 30:1

This table serves as an introduction of what is to come. First, we will explain what causes a compost heap to go cold. Then, we will talk about the signs that indicate that a compost heap has gone cold. Finally, we will also discuss some solutions to get the compost heap warm again and prevent the compost heap from going cold in the future. 

1. How Does a Lack of Airflow Cause a Compost Heap to Go Cold?

As we have mentioned, the key to having a good compost heap lies in the number of bacteria in the compost, breaking down the plant materials. There are aerobic and anaerobic bacteria. While both work at breaking down organic materials, aerobic bacteria does so much quicker. 

If you only have anaerobic bacteria working to make compost, the process will be much slower, and you might have to wait up to two or three years for the compost heap to produce compost. Therefore, it is essential to have aerobic bacteria working on the organic materials. As the name suggests, aerobic bacteria require airflow and oxygen to function correctly. 

Signs That a Compost Heap Doesn’t Have Sufficient Airflow

If you notice that your compost heap looks very dense and matted, it is a sign that there is not enough airflow in the center of the compost heap. The plant materials will also take longer than usual to break down because there aren’t enough aerobic bacteria working toward breaking down the plant materials. 

How to Fix a Compost Heap With Insufficient Airflow

As you might guess, the solution to an airflow problem is relatively simple. First, you must introduce more air to the center of the compost heap. This will encourage the aerobic bacteria to function properly and quickly break down the plant materials. 

To introduce more air to the center of the compost heap, you can use a pitchfork to turn over the compost heap and “fluff” it up a bit. Doing so will introduce more airflow throughout the compost heap and help the bacteria to work better, heating the compost heap as they work. 

Preventing a Lack of Airflow From Causing Cold Compost

In most cases, including this one, prevention is better than cure. To prevent your compost heap from going cold due to a lack of airflow, you must ensure that there is always sufficient airflow throughout your compost heap. To do so, you must use a pitchfork to turn your compost heap over every two weeks. 

2. How Does Too Much Water Cause a Compost Heap to Go Cold?

Too much water causes a compost heap to go cold because it causes the compost to become anaerobic. Spaces filled with water do not have air. Therefore, the compost heap will not have enough air to support the aerobic bacteria from functioning correctly. 

Signs That a Compost Heap Is Too Wet

There are a few indicators that a compost heap has too much water. However, the best indicator is a foul smell. A healthy compost heap will not have a particular smell and might have an earthy aroma. However, a compost heap that has gone anaerobic due to too much water will have a rancid odor.

Another indicator of a wet compost heap is a slimy texture. Instead of breaking down, the leaves and other organic material will develop a slimy surface, and the composting process will be slowed down even further. 

How to Fix a Cold Compost Heap Due to Too Much Water

The fastest way to fix a cold compost heap due to too much water is by turning the compost heap, allowing more air to fill the spaces. Also, add some absorbent materials into the compost heap that breaks down quickly. Sawdust or ash are great examples of materials to help fix a wet compost heap.

These materials will encourage the aerobic bacteria to speed up the composting process, heating the compost heap again. 

Preventing a Cold Compost Heap Due to Overwatering

The Best way to prevent a compost heap from getting too much water and going cold is by limiting the water that gets into the compost heap. This might mean that you cover the compost heap during the rainy season and only water it once or twice a week. 

3. How Does Carbon-Nitrogen Ratio Cause a Cold Compost Heap?

A compost heap’s ideal carbon to nitrogen ratio is 30:1, meaning 30 parts carbon for each part nitrogen. Carbon can be found in dry organic material, such as sawdust, dry leaves, or ash. On the other hand, nitrogen mostly comes from raw organic materials, such as cut grass and kitchen waste. 

Maintaining a correct carbon-nitrogen ratio in a compost heap is crucial to ensuring the compost heap is aerobic and the bacteria can work effectively to break down the materials. 

Signs a Compost Heap’s Carbon-Nitrogen Ratio Is Incorrect

The most significant indicator that a compost heap’s carbon to nitrogen ratio is incorrect is when dry leaves or other dry materials take too long to break down. For example, if it has been a few months since you added dry leaves to the compost heap and they are still not broken down, you should suspect something is amiss. 

How to Fix an Incorrect Carbon-Nitrogen Ratio in Compost 

The best way to fix an incorrect carbon to nitrogen ratio in your compost heap is to add more carbon materials to the compost. Sawdust, dry grass, pine needles, or dry leaves are excellent carbon sources and can fix your ratio problem easily. 

Preventing Carbon-Nitrogen Ratios From Making Compost Cold

To prevent a compost heap from going cold because the carbon to nitrogen ratio is incorrect, you must ensure that the balance is right. For example, ensure that there are approximately twice as many carbon materials in the compost heap as nitrogen materials. Also, ensure your compost heap gets sufficient airflow and water. 


A compost heap goes cold because of factors that make the compost heap anaerobic, causing the bacteria in the compost heap to work slower. To ensure your compost heap remains warm and the bacteria work effectively at breaking down the materials, you must ensure your compost heap has enough airflow, not too much water, and a 30:1 carbon to nitrogen ratio.

If any of these three factors are faulty, your compost heap will go cold. However, fixing and preventing these problems is not difficult. You should be able to save a cold compost heap without too much effort.

Alexander Picot

Alexander Picot is the principal creator of TheGrowingLeaf.com, 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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