How to build a tumbling composter

When I first moved into my current home last August, I really wanted to compost. I built a bin out of wire fencing that I bought through craigslist and constructed a cylinder of sorts using concrete blocks (my favorite gardening material at the time, if you look back).

See? Concrete blocks work for everything.

We didn’t do the best job keeping up throughout the winter… we’d bought some sort of specialized kitchen container for compost from Ikea, filled it a few times and found the kitchen smelly. Eventually I was carrying out compost on the most random occasions, when it suddenly came to mind or when someone I was making dinner with asked what they should do with the onion skins.

I was surprised when, this spring, the volume in the bin had actually shrunk (something it is supposed to do, as organic matter breaks down and transforms brown and green waste into healthy soil).

You’ll have to trust me, the pile is totally smaller.

But even so, I knew the system wasn’t perfect. The bin was in the back, at the alley, near the trash and recycling. My well-intentioned but somewhat lazy household of roommates cycling in and out would do better with something right outside the door (which incidentally opens to the kitchen). And my beautiful but perhaps temporary garden would do better with compost that finishes quickly. Out of this, my job (as local foods outreach coordinator for the University of Minnesota’s Student Organic Farm), and the public community education system (I taught a class about it last weekend), our tumbling composter was born.

Tumbling compost barrels create usable compost, called humus, after three weeks to six months — a long range, but a much shorter time nonetheless than the one to three years that a regular compost bin produces. This is because in order for the waste that compost is made of to break down, it must be turned, about once a week, with a pitchfork.

These handy devices can be bought. I recently saw one for $79.99. They can also be made. To my surprise, it was incredibly easy.

And isn’t it pretty?

Here’s how to build it.

You’ll need (materials in parentheses optional):
Plastic drum / trashcan / etc.
PVC pipe / metal pole / etc.
Six 2 x 4 pieces of all-weather lumber
Sheet metal ¼ the length of the barrel
Two knobs
Nails
Hammer
Electric drill
(Carpenter square)
(Permanent glue)
(Three hinges)
Bolts

1. Build the base. Place two pieces of lumber so that they form an X. Use the carpenter square to make sure they are square, then nail the pieces together in the center. Repeat this with two more of the boards. You now have the two ends of your compost tumbler base.

2. Support the base. Stand one of the “X” ends up then attach the remaining board to one of the legs and attach the other end of the board to the bottom of the second “X” end. Repeat with the last board and to the back of the base (see below how it fits together).

3. Make your barrel spin-able. Turn the barrel on its end. Drill a hole slightly larger than the diameter of your pipe or pole in the center. Repeat with the other side of the drum. Slide the metal pole inside the drum to act as an axle so the drum can spin.

4. Make the door. Put the barrel back on its side and cut a rectangular hole in it. Save the piece of plastic you removed. Attach three hinges equidistant apart on the drum at the top of the hole you just cut. Glue one knob to the plastic piece you cut and another to the drum itself opposite the hinge side.

(We actually did something much simpler: just cut three sides of the door, attached one knob on the outside, and are holding it shut with duct tape, which must be refreshed from time to time.)

5. Make a mixing fin. Bend the piece of sheet metal in to an “L” shape. Use the drill and bolts to attach the fin inside the drum on the opposite side of the door.

(We actually skipped this step, but it seems like something that wouldn’t be hard to add at any point.)

6. Assemble your composter. Place your new composter on the “X” base you created in and check how well it spins on the axle. Paint the drum a dark color if it is not already; this will help content heat up and speed up the process.

Finished composter, community education workshop participants standing proudly.

Side note: I imagine you could doctor this design in many ways. For instance, we thought adding some support at the top of the Xs might be a good idea.

7. Use it! Fill the tumbling composter with compostable material. Add water to the drum to moisten the contents. Turn the composter a few times to mix the ingredients and continually check on and tumble the compost. Put it outside your kitchen door — you’ll be much more likely to use it.

And there you have it. Stay tuned for more composting fun — I’m getting into building with pallets.

Happy spring!

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About PRI Cold Climate

PRI Cold Climate is an organization centered in Minneapolis that promotes permaculture throughout the region, fostering sustainable lifestyles and communities. We design and demonstrate permaculture systems specific to colder climates like ours, and provide leadership and resources for the permaculture community.
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