When we redesigned the layout of our home garden plot last fall, I designated some space to build a larger and more central set of compost bins. This month, I made some time to assemble these new bins, so now I have some pictures and construction details to share with you about this project.
After building and working with several different types of compost bins over the years, I have observed that any weaknesses in bin materials or design will eventually lead to the destruction and/or ineffectiveness of the bin. So in this case, I was motivated to build a set of bins that would work well and stand the test of time. Could I build a free compost bin with few old pallets? Yes. Could I whip up a portable composting receptacle in a few minutes with a roll of wire mesh? Yes. Could I create a compost pile without any supporting structure at all? Yes. These options just didn't satisfy our top priorities of function, longevity, and aesthetic appeal. Personally, I would rather pay for a compost bin that looks good, functions really well, and lasts a lifetime.
Before we dig into some of the finer details, here's a video summary of the build process to give you a quick introduction to the methods and materials used.
Most compost bins are too small. It's not often that you'll catch me saying that something is better when it is bigger, but in the compost world, I think this reasoning holds true. Bigger compost bins have two significant advantages. One is that larger volumes of compost are better able to build heat during the composting process, which accelerates decomposition and kills pathogens. Therefore, larger compost piles can breakdown organic matter faster and more effectively than smaller piles. The second advantage of larger bins is that they have the space to accommodate all of the bulky organic material you'll be adding, even during those big harvests or garden clean up days. If you can't put this material directly into your compost bin, you'll need to have another space, so it seems simplest to just use the same space and make sure it is big enough.
Each chamber of this new compost bin is 4 feet wide, 4 feet deep, and 4 feet high. That gives us a volume of 64 cubic feet or 2.4 cubic yards to work with in each chamber. This is a significant increase in volume over the more common 3 foot by 3 foot bins. At first glance, a 1 foot increase in the linear dimensions doesn't seem like much, but those 3 ft bins only have a volume of 27 cubic feet or 1 cubic yard.
Multiple chambers are oh so helpful when managing the composting process so there was no question that the new system must have several chambers. We need a designated space for collecting cover materials (bulky odour free organic matter like leaves, weeds, and grass), a space where a compost pile can sit undisturbed for a year to finish, and a space to build a new compost pile while the old pile is finishing. That said, the 3 chamber bins I have used in the past have often left me looking for a little more space at times, either because I needed more room for bulky cover materials or more time to let a completed compost pile age. Therefore, I opted to step it up to 4 chambers this time around.
Partially removable side walls are also a pleasure to have for those times when we want a barrier in place but not the whole wall. For example, when a new pile is just started and we are digging holes in the centre of the pile to add new deposits of fresh organic matter, I would rather not have to do so by reaching over a 4 foot high wall. Also, when we start to empty a finished chamber, the shovelling is made much easier if the front wall is lowered progressively as the compost is removed from the top down. If the whole front wall has to be removed as a single unit to shovel out the compost, some of the compost will inevitably spill over in front of the bin and make it more difficult to reinstall the front wall unless the entire bin is emptied.
All of the wood composting bins I have built and used in the past have rotted away to various degrees. I wouldn't mind the idea of replacing a few boards once in a while if it was easy, but the boards that rot first are always in the lower and least accessible regions of the bins where conditions are most favourable for rot. It is a compost pile after all and no organic matter is immune from natural decomposition. It has become clear that if I want to build a compost bin once and only once, then a different material choice is necessary. Thankfully the decision to avoid wood was made easier by the huge increase in lumber prices this year! I considered the possibility of concrete, plastics, and even stone, but galvanized metal came out on top. It allowed quick assembly with a comparable cost to wood. The total cost of the materials we used was $1050 while a similar bin built with cedar posts and 2x6 spruce lumber for the side walls would have come right around $1000 as well.
17 Gauge Galvanized Metal Fence Posts 1 7/8" x 6'6" ($21.99 each x 10)
Galvanized Post Caps ($1.99 each x 10)
9 sheets of 29"x 8' corrugated metal siding 7/8" thick ($347.65 total)
25 Gauge Galvanized Stud 1 5/8" x 8' ($6.53 x 13)
Pan Head Self-drilling Metal Screws ($8.69 box of 100)
5/4 inch x 8 foot Cedar Decking ($23.19 each x 18)
Total Cost $1050 CAD
Skill Saw with Metal Cut-off Blade
Radial Arm Saw
Sledge Hammer and Trailer Hitch Ball
The framework of the bin is provided by 10 metal posts. Each one was carefully pounded into the ground and levelled. I wanted these posts to be anchored in the ground so their rigidity would keep the chamber bays straight even when the front walls were removed. If the posts merely sat on the surface, the corners would lack the stiffness needed to maintain a good fit for those sliding boards. I am not sure if the posts will stay straight enough over time, but if necessary, I can always pop a few screws in the top board of each chamber to keep the posts the same distance apart.
Galvanized metal channels were screwed into each post to support both the corrugated metal side walls and wood front walls. These U-channels are not made for this purpose, but their dimensions fit the bill nicely, and they have a much lower cost than the J-channels that are typically used to finish the edges of corrugated metal walls.
The corrugated metal wall panels have a width of 7/8 of an inch and slid nicely into the 1 inch wide gap in the metal U-channels. At this point, I was really thankful that I had taken the time to level the posts, because this process wouldn't have gone as smoothly if the gaps between the posts were uneven. The metal is a solid material to build with, but unforgiving with the measurements don't add up.
The wood boards for the removable front walls also fit the U-channels perfectly because they are 5/4 inch deck boards, which have an actual thickness of 1 inch. I might have used some cheaper 1x6 spruce lumber here but it's thickness is actually only 3/4 of an inch and I wanted things to be snug. Since the 5/4 inch decking fit so perfectly, I went that route. This bumped the cost up a bit because the untreated 5/4 decking was only available in cedar. The lifespan of these rot resistant cedar boards could be significantly longer though so maybe the added initial cost will pay me back in the future by lowering replacement costs.
If you were hoping for full instructions on how we plan to use these new compost bins, I'm afraid I need to leave you hanging for the moment. I will share more about that once we have had these new bins in use for a few seasons. If you don't want to wait that long, I will be teaching this subject in Module 8 of our Seed to Table course. I would also highly recommend checking out the work of composting master Joseph Jenkins. If you have got any additional questions about the construction of these bins, send them to me using the contact form at the bottom of this page and I'll add the missing details to this post.
After building these bins in the location described and beginning the filling process, two things happened. One, our neighbour expressed concern that there would be more mice in his house because of this compost bin. Two, the galvanized channels proved to be a bit too flexible to restrain the outward force of a full bin without bending. So, shortly after building the bins that I thought I would never have to build again, I found myself building them again. I relocated them to the only other logical location on our property and made the video below to better explain the build process and upgrades. Enjoy.