$2 DIY compost thermometer

Hard core composters thrust their naked arms into a compost pile and grunt accordingly to determine how hot and hard the pile is working. The more squeamish composters can rely on compost thermometers. You couldn't pay me enough to thrust a naked appendage into my compost pile right now - maybe in a month. For a few days, my compost pile smelled bad. Reeeaaaally bad and I needed a quick way to fix things before the neighbors got out the pitch forks.


My pile turned anaerobic when I added a bunch of neglect and kitchen scraps saved over the winter to my compost pile. I have a pretty basic compost bin right now that makes turning my pile difficult, so I started trying out different techniques of aerating. To help guide my approach, I quickly rigged up a cheap DIY compost thermometer. The basic idea is that the hotter the pile, the better it is working.

fridge-thermometerMost decent compost thermometers will run you at least $30 because they are long enough to reach deep into the pile. I already had a $2
digital thermometer for a fridge that I ordered off ebay a while ago and I quickly converted it into a 1 meter compost thermometer with some duct tape :)

I've been using it for a while now and am happy with it. The display takes a couple minutes to stabilize so I just put it in the pile and go putter in the yard for a while. My $2 thermometer seems to be accurate to about +/- 2°C or better which is more than sufficient for my needs. Don't forget to take it out of the pile before it rains! I'm sure the display part isn't water proof, but you could probably seal it up in a ziplock if you were inclined. I put mine back in the shed after every use.

The hottest I've seen my pile was about 41°C a few inches below the top surface. I always thought the center would be hotter, but I've got an old pile where there probably isn't as much action further down. I'd love to see my pile consistently at 55°C to 65°C so that I could do "hot composting" and break it down super fast, but I'll need a better bin setup and likely a fresh start with materials. FYI: this post was originally written in early spring.



I built a much improved compost thermometer here!

compost thermometer in grass



<< click on the picture to see how to build the new

and improved compost thermometer.





  1. Jerry says:

    I tried doing something similar, though my test didn't quite work as well as yours!

  2. Adam Fraser-Kruck says:

    Hi Jerry. I've updated the post with a new link on how to build an improved compost thermometer. What did you end up doing with yours?

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