A great question from Marie:
I used to do worm composting when I lived in Washington state. Now that I have moved to Arizona, and it is approaching summer, I am concerned about temperatures too hot for worms. I don’t have space to keep a bin inside, so that isn’t an option. I was thinking of using a container garden that I built using large concrete blocks. (The rectangular kind with two big holes in them that are used for walls). It is 2 feet x 6 feet wide, and 2 feet deep. It is shaded during quite a bit of the day by a large citrus tree. It gets regular water through a drip irrigation system. I was going to use a thick layer of pine needles to cover the top and encourage the worms to move deep into the center of the bin. Do you think that this would work?
Thank you for your expertise!
You are 100% correct in assuming that outdoor vermicomposting during an Arizona summer will likely be very challenging. But the good news is that the idea you shared sounds very much on target in terms of the sort of system that could potentially work!
For the benefit of others reading, I am going to start by laying some groundwork based on what we are dealing with here. To be honest, I don’t really know how hot it can get during an Arizona summer, but I’m am going to guess that 100+ F is pretty common over the course of several months.
Short of setting up some sort of power-sucking, artificial cooling system, typical free-standing enclosed plastic “worm bins” are just not going to work. Wooden systems, and other breathable systems (eg Worm Inn) might be possible under the right circumstances. Lots of shade. Lots of air flow. Lots of moisture.
The one nice thing about Arizona is the low humidity – this makes it easier to employ evaporative cooling strategies.
Just so you know, the worms can likely survive at temps up to about 94 F – but keep in mind that temps inside a vermicomposting system can often be even warmer than ambient temps.
OK let’s chat about your idea…
What I love about the idea is that it is close to the ground, open, sheltered (in terms of location and materials used), and irrigated. That sounds like a magic combination to me!
That said, there are likely still a couple of tweaks I would make:
1) Instead of pine needles, I would likely use straw/hay or something like layers of burlap (latter might work really well for evaporative cooling). The needles will probably be a pain to work with and they will increase acidity and maybe add resins to the bed that aren’t all that worm-friendly.
2) Something to think about before you set anything up is creating a decent pit down below. The earth itself serves as an amazing buffer against extreme temperatures (both hot and cold). If you dig down a couple of feet and add lots of moistened cardboard (brown corrugated cardboard is probably my favorite – and I think the worms agree), this will provide the worms with a place they can retreat to if conditions in the main bed end up getting too hot.
But like I said, you are absolutely on the right track!
Hope this helps – and please do keep me posted on your progress.