Vermicomposting in Arizona Summer Heat?

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!

Hi Marie,
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.

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    • Walt Pendleton
    • May 11, 2018

    I have lived in Arizona for many years. I set up a in ground worm bin 4 x 8 foot. with concrete blocks. I put a wire hardware cloth to keep varmints out. I got shredded newspaper and covered it with old rugs.
    I have extra worms if anyone in Arizona wants them.

    • don
    • May 11, 2018

    Hi Walt, Where in Arizona are you? Do you sell castings?

    • Bentley
    • May 11, 2018

    That’s great, Walt (and great to hear from you)
    Thanks for chiming in!

    • Walt Pendleton
    • May 12, 2018

    I am in Surprise Arizona. I do have worm castings as well as worms.

    • Walt Pendleton
    • May 13, 2018

    Give me a call if you want free worms or castings. 623-734-5097

    • John W.
    • May 13, 2018

    You can also set up a Sprinkler system. I had a mister that turned on for 15 min once an hour. It was long enough that top layer got wet but short enough that the worm bin did not get overly wet. You would have to play with the setting with the system you might get. I liked the mister (kind of like the ones they have at them parks that just keep people from passing out), because water in my area is not cheap. Just bought a digital timer that let me adjust when and how long and I was done.

    • Marie
    • May 14, 2018

    Thank you all for the tips. I will use a different mulch and add a couple extra misters to the drip system.

    • clare
    • June 28, 2018

    I want to set up some worm towers in my garden in spain, 45Km inland from Malaga. Do you know where I can bbuy worms which will withstand the heat annd can you make suggestions as to how to go about it.
    thank you

    • Bentley
    • July 11, 2018

    Hi Clare,
    In ground systems like worm towers are likely your best bet for beating the heat, so that was a good idea. Unfortunately, there are no composting worms that are especially well-adapted for really hot conditions, but assuming your towers are deep enough in the ground, I would think you could get Red Worms to survive ok. Maybe keep a small indoor “insurance bin” just to be on the safe side. Here is an article I wrote on the topic:

    • Shaul
    • August 17, 2018

    Solar-reflective, Mylar plastic sheeting works great at cutting temperatures. Position it over your bins wherever the Sun will hit and if you can have it not touching the bin, so that there’s room for airflow, then even better.

    • Caleb
    • January 4, 2019

    @Shaul – I LOVE that idea, I never thought about that! Mylar sheeting is used all the time in indoor grow tents to keep the light reflecting in the tent, but I didn’t think of it for reflecting the outside of the worm bin! I’m totally going to line the outside of my WF360s with mylar sheeting now great idea!

    • Shaul
    • January 4, 2019

    Caleb; I used to work in a large warehouse for a company that supplied pharmaceuticals and beauty products to pharmacies. Many times, pallets of cartons containing heat-sensitive products, would arrive covered with Solar-reflective Mylar plastic sheeting. Since the company considered it a waste product, I took it home. Now it’s being repurposed keeping wormbins cool in summer and warm in winter. Try to keep a few inches between the Mylar and whatever you’re covering to allow for airflow.

    • Bentley
    • January 8, 2019

    Fascinating topic guys!
    Shaul – I would love to see a comparison of temp readings (with and without the mylar). Maybe set up dummy bins (or at least one for the full exposure treatment) just to make sure no worms get cooked in the process.

    • Palobrea
    • July 4, 2021

    To combat the heat, I live in Tempe/Phoenix, AZ, I am using the Bokashi method. It is an anaerobic composting style that uses fermentation to speed up food break-down. What I most enjoy is the ease in composting all food types. I can compost rotisserie chicken to plantain peels etc. I use the bokashi grain/although there are many videos to create your own either using cardboard shredding or some yeast activator. That said, you do have to get into the habit of digging trenches to bury the contents of a bin after the fermentation period – 2 weeks or more. I came here to see if there was any luck with vermi-composting in our extreme climate – and it sounds like there might be some success. I’d like to look into a combined process of Bokashi and vermicomposting. Vermi in my case, would be the post process. I love the bokashi method, however, I’m not sure if I’m wrongfully expecting to see black loamy soil 🙂 my soil here in very clayey and red, so perhaps it won’t get black but I wonder if an introduction of worms could help create that. Another added benefit of the bokashi is there is not a putrid smell which I am very thankful for – granted I compost meat. Anyway, if anyone has some input on this idea of combining the two processes, please kindly share. Otherwise, I found some useful tips here to try, thank you.

    • Bentley
    • September 1, 2021

    Hi Palobrea – thanks for your feedback! You have made some very important points. I think a lot of people have the mistaken impression that bokashi is some form of composting (and it is often labelled as such) when in fact it is – as you say – a type of fermentation process. As such what you get at the end, as pleasant as it is compared to a rotting bin of garbage, isn’t yet garden-ready per se. You can definitely pair bokashi nicely with worm composting and various other aerobic composting methods and end up with some really nice stuff – but it is always going to take some time. My suggestion would be to combined the bokashi bucket stuff with a much of bedding materials (eg shredded cardboard) and maybe some form of “living material” (eg aged horse manure) and let that sit for a bit independently. If you set up a more typical worm composting zone close by they will almost certainly start moving into the bokashi zone once it is to ther liking. Once you have the worm habitat established, moving forward you could likely just add any new bokashi deposits up top and the worms can move up into it on their own schedule. I do recommend adding some form of bedding to soak up the liquid component as much as possible though – a lot of that pouring down into the worm zone may cause harm.

    • Palobrea
    • September 2, 2021

    Thank you Bentley for the wonderful suggestions. I will look into the combinations you mentioned.


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