Compost Temperature: Is your compost hot enough?

Compost.  We really should all be composting.  It’s great for the environment.  It’s great for your garden and there are so many different ways to go about it.

If you’re lucky enough to have a yard, then a compost pile is a pretty simple and easy way to go.  Read this post from over a year ago about a simple 3-bin composting system.  The author talks about the importance of heat in a healthy composting system, but never gets into the importance of actual, specific temperature.

Is your compost pile hot enough?  What is your compost temperature?  Do you know?  Do you care?  Should you care?

Compost Temperature: Why do we care?

To put it simply, yes, you should care about the temperature of your compost pile.

Checking and monitoring the temperature of your compost pile is important in order to ensure that enough heat builds up to kill off weeds, their seeds, disease, parasite and the like.

How does this happen?

When provided enough nitrogen, bacteria, and fungi within the compost pile will grow and reproduce rapidly – thus breaking down and decomposing the organic material and producing heat.  You want this growth and reproduction because you want the material to break down and give you nutrient-rich compost.


Compost Temperature: What should it be?

To ensure that your pile has composted properly, it needs to reach the desired range of 140 degrees to 160 degrees for 10 to 15 days.

However, watch out.  Some piles can get REALLY hot and reach temperatures at or above 180 degrees.  When piles get this hot, they may spontaneously combust.  In order to prevent this, monitor your pile’s temperature and aerate it when if it reaches 165 degrees.  The simplest way to aerate the pile is to turn it.  This also ensures that pile is getting hot evenly and all the material is being decomposed at the same rate.

In a perfect world, a pile would be aerated by turning it at least 5 times during the 10-15 day range.

How do know what the temperature is inside the pile?

The easiest way is by procuring a compost thermometer.

Simple and cheap, a compost thermometer is good thing to keep on hand to give you the piece of mind you need to be sure that you’re compost temperature has reached and stayed where it needs to.

Compost Temperature: What if mine never reaches the right temp?

On the opposite spectrum from combusting, some compost piles might never reach the desired range.  If you’re pile never reaches 140-160 degrees, you cannot be sure that pathogens and weeds seeds have been destroyed.  This can (and probably will be) bad news for next season’s garden when you spread this fresh compost on it.

In this case, your pile needs more nitrogen-rich material.  This includes things like fresh grass, plants in the legume family and fresh manure.