Building a three bin compost system

Plus, experimenting with location and a quick audit of the designs I've tried—and why a lot of them don't work.

a pic of me at work.

Hello,

It’s been a month since you’ve heard from me. In the two years that I’ve been writing this Substack, I don’t think I have ever let that much time go by without sending you a letter. Mea culpa, mea culpa. Life got very busy. I’ve got my first private clients, I’ve been teaching classes to kids, I’m preparing lectures for a college and workshops for a women’s group, and I’m working on an expansion of “Compost This Book” with Timber Books. I’ve never been happier, but I’ve also never been so behind. I haven’t answered an email in like two weeks.

What have I been doing?

Mostly building compost bins. Also, learning how to design and build compost bins, and also (also!), learning how unreliable the internet is at offering up solid and affordable blueprints for compost bins. Try to search “three bin compost design” and what you get back … isn’t very great. Some designs cost an outright fortune to build. ($900!) Others are cheaper, but often contain puzzling oversights and unnecessary complexities. Many do not effectively account for the reality of working an actual compost. Too many have front slats that fit flush, when you want front slats that are easy to wiggle in and out each time you need to turn the compost. Some don’t account for the width of the interior walls when they size out the backboard, meaning the individual bins ended up smaller than a good pile requires. Another frequently overlooked feature in the designs I found was basic support for the bin walls. Compost is heavy. As you build a pile, it begins to weigh a lot. Without structural reinforcement, the sides of a bin will strain and bulge, leaking ooze, and eventually come apart.

A bin that is falling apart. The culprit? Lack of structural support on the sides and front slats improperly fitted to front braces.

So, I threw out all the blueprints I found online and made my own, with a strong assist from friend of the garden and renowned hairdresser (twist!) Kevin Spring. Kevin asked me lots of questions about how compost is meant to work, sat over my shoulder as I audited blueprints, and helped bumper lane me into creating something that was realistic to build and would work to make compost. Then he went to the hardware store with me, bought the supplies, and helped me construct the thing.

The design that we arrived at utilizes a minimal amount of wood, requires a minimal amount of cuts, and otherwise requires only exterior screws, hardware mesh, and staples. The sides are reinforced with 2x4s, but leave enough open mesh to accommodate airflow. The backboard is extended in length, in order to allow each bin to be a true 3x3 ft. I did not end up including a lid because large animals in my area are not a concern, in addition to what it saved us in cost. If you endeavor to build this system, keep in mind that I wrote a guide to *running* a three bin system not that long ago. You can find that edition here.

Note: The three-bin system is generally comprised of three bins that are 3x3x3 ft, as this is considering the ideal size for well-functioning decomposition. You could make the size of your bins larger, but I don’t recommend it. The bigger your bins, the larger your pile, the heavier everything gets, the more likely you’ll deal with compaction, and then the more likely you have bad smells. Save yourself that trouble.

Completed build

Bin in progress, with an assist from Kevin (friend of the garden)

One thing to consider if you do end up building a three bin is where it should go. I’ve written before about how the location of your pile can make or break your compost practice, and this holds true for the three bin system, although there are some additional considerations here. You’re likely to want a place where the bins aren’t cramped into a corner and there’s at least some room nearby to heap materials as they’re waiting to be added. You also want to be able to wield a shovel freely, so avoid areas with low-hanging branches or spiky bushes. If your yard, like mine, offers barely any space, just do your best. Your best is enough.

If you’re nervous and you want the option to experiment with where your three bin should be located, I’ve also designed something I call the “MVP” Three Bin that could help you out. It it first started making an appearance in my work with private clients, where evolving landscape designs and other concerns meant a permanent location was sometimes difficult to pre-determine.

To build one, you only need a set of eight yard stakes and a roll of hardware mesh or chicken wire. The stakes should be at least 4 ft tall. Place the stakes in rows of two, about three feet apart. Then, unroll the hardware mesh and snake it through the stakes in an elongated “S.” When you’re done, pinch the corners into a proper square-shape. (See picture, below, you’ll get exact what I mean.) Then see how good—or not—the bin system feels to use in that location. Give yourself about a month with it. Don’t like it? Move it somewhere else in a jiff. When you find a spot you like, you can build a sturdier system in its place. Reuse the hardware mesh or chickenwire when you do. Or just leave it as is, altogether.

The MVP bin at the house of a private client.

For the build above, I located the bins in the garden, but near the kitchen door, while using the fence to provide a little bit of discretion. Since this particular client has a large house and frequent guests, I wanted to ensure the compost was obvious enough to be accessible to first-time visitors, but not overly obtrusive for the homeowner. We’ll give it about two months to sort itself and see if we like it, but so far it’s been great. Every time I come by to check on things, there’s at least one or two interested people milling about with eager questions and expressing excitement.

If you would like to improvise your own three bin system, I wholeheartedly recommend rolling your sleeves up and getting into it. Just know that each bin should be the same size, that size should be roughly 3x3x3 ft, the sides should both accommodate airflow and offer structural support, the front of the bins should “open” to accommodate easy turning, and the bottom should simply be open to the earth. The lid is optional. As long as your bins align with those basic principles, you’ll have a pretty well-functioning system.

My original “designs” for the system we built

A note for men:

The hardest battles I have ever fought in my life are with men who insist they must over-engineer a compost bin. They always start simple, get excited, and then want to add a bunch of bells-and-whistles. “A bigger pile will be way cooler, wouldn’t it?” they’ll say. Or: “What if we made it look like a spaceship that spun continuously on a motor?” Or: “What if we..” etc. Contained within this enthusiasm is the well-intentioned desire to “improve” the compost through technological innovation, but the truth is there is no “improving” on such a fundamental, tuned-by-centuries ecological process. The system must self-create in order to generate its own capacity. Beyond that, if the project gets too complicated, it ends up abandoned halfway through and then no compost is made regardless.

Simplicity is always key.

Love,
Cass