Use a Compost Thermometer Increase Your Compost Quality

If your goal is high quality compost, learn why a
compost thermometer is a must-have tool.



You've heard about them, but have you ever used one? They'll tell you a lot about what's going on inside your compost pile. For instance, based on their numbers, you'll know exactly when specific types of microbes are active. Not only that, you'll also know exactly when to turn your pile. So what is this wonderful tool?

It's a compost thermometer! And you must have one if your goal is to produce high quality compost in the shortest amount of time.

This page will provide detailed information about the following topics:

Why Your Compost Pile Heats Up

The answer lies in one very complex word - Microbes! Okay, we'll leave it at that. Just kidding.

Assuming you've started with the proper organic composting ingredients, moisture and oxygen levels, and volume of materials (approximately 1 cubic yard), your compost pile will start to heat up within a day or two.

This heat is generated by all of the microbe's metabolic activity (i.e. eating, excreting, breathing, and multiplying). The majority of the heat comes from bacteria; however, some fungi and larger soil organisms also add to it. Below, we'll get into the various temperature stages in your compost pile as well as the specific microbes that are present at each stage.

Not all compost piles heat up. Piles that are built slowly, over a long period of time (continuous composting), don't tend to heat up as much compared to piles that are build all at once (batch composting). This is one of the reasons why piles built using continuous composting take so much longer to decompose.

The Temperature Cycle of Compost

Compost Thermometer Temperature Graph




The above graph illustrates the typical heating cycle of a well-made aerated static pile of compost. That is, a compost pile that was build properly, and turned at the necessary temperatures. In order to achieve this type of heating cycle, a compost thermometer is a must.

A well-made compost pile will go through distinct three phases. First, it will enter into the mesophilic stage (68-104 degrees Fahrenheit). Second, it will enter into the thermophilic stage (105-150+ degrees Fahrenheit). Finally, the pile will enter into the maturation stage (not indicated on the graph). More on this stage below.

Please note that specific microbes are present at each of these distinct stages. For example, certain types of bacteria thrive in the thermophilic stage, while certain fungi thrive in the maturation stage.

The points labeled A, B, and C indicate when the pile was turned. As you can tell the pile cools off slightly after being turned. Therefore, turning your pile according to your compost thermometer readings not only introduces oxygen back into your pile, it also helps to reduce the temperatures (temporarily).

Is Your Compost Ready to Cure?

Typically, your pile is ready to cure when it fails to reheat after being turned. This occurs after point C in the above graph. How can you determine this point in your own composting adventures? Use your compost thermometer. We told you it was a handy little tool.

At this time, the microbial activity in your pile has slowed down, which means there is no need to keep turning it. Curing typically lasts three months or longer.

Sterilizing Weed Seeds and Pathogens

To sterilize weed seeds and kill pathogens you'll want to abide by the following rule - Keep your compost temperatures in the range of 140F and 150F for at least 3-4 days.

That being said, you want to make sure your pile doesn't go above 150F for more than a couple hours because you will start to kill off some beneficial microbes.

The best way to ensure your compost will be free of weed seeds and pathogens is to monitor it using a high quality compost thermometer.

Qualities of a Good Compost Thermometer

  • Appropriate length to reach the center of your compost pile
  • Clear, easy to read display
  • Made of stainless steel or other non-rusting material
  • Includes a warranty
  • Temperature range from 0-200 degrees Fahrenheit
  • Display is hermetically sealed, preventing fogging

Find the Best Thermometer for Your Needs

We've divided our recommendations up into backyard and commercial composters.

Thermometers for the Backyard Composter

Thermometers for the Commercial Composter