This is the easiest and cheapest composter design we've come up with for keeping rodents out of our compost. We made the traditional compost bin out of pallets but rats crawled through since we didn't line it with mesh. Instead of building another pallet bin and lining it with mesh, we skipped the wood all together and built a cylinder of mesh.
The composter consists of two parts: an outer basket containing wood chips and an inner cylinder of compost that is always topped with carbon material and a mesh lid if we're really worried about critters.
The outer ring of wood chips surrounding the compost chamber insulates the compost, absorbs any smell from the compost and makes it harder for critters to reach the compost. Who wants to bite through wire mesh and then crawl through a foot of woodchips to eat rotten fruit? Hopefully no one. Not even you, neighborhood possum.
The inner ring of compost has decomposed very fast, it sinks about a foot every two weeks. The woodchip area is also full of mycelium and a mushroom or two pops up every month.
Our last composter (pictured with me here) also featured a fan to aerate the compost using a solar hot air collector. You can check out more about our composting experiments at our blog for decentralized waste management strategies.
We also have a temperature probe in ours (see blue cord) to see how hot it is.
Step 1: Equipment and Materials
To build a 4' wide composter with a 2' diameter inner cylinder that's about 3' tall you'll need:
12.5' x 4' quarter inch galvanized mesh or as the hardware store calls it "hardware cloth"
3' by 6.28' mesh or fencing to separate inner compost chamber from woodchip insulation. (we found old 4' wire fencing)
2" or longer wire pieces to piece mesh together (or zip ties)
wire cutters (it's such a pain to do this if you don't have good wire cutters)
Composters need to be big enough to allow the material to get hot and stay hot. This can be achieved by building an uninsulated composter that's 1 cubic yard or it can be samller if it's insulated to keep heat in.
Size of mesh needed for Smaller composter that's only 3' diameter with inner basket of 1'. For this one the composting chamber is only 2' in diameter but it's insulated on all sides by 1' of woodchips. My drawings refer to dimensions for this smaller composter.
7' by 4' of quarter inch galvanized mesh for outer compost container
3' by 3.14' cheap mesh for inner cylinder
Why make a smaller one? Because space is expensive.
Step 2: Make Angle Template
Creating a nice cylinder with a folded bottom is easy and it creates a beautiful star shape. The trick is to calculate exactly how many degrees each tab needs to overlap to create a circle.
The thing to know is how many tabs you want to cut. If you want to make 6 tabs, then divide a 360 degrees by 6 to find out how much each tab overlaps. 60 degrees! The more tabs you use (12 in this photo) the more circular the cylinder, which means it'll be a stronger shape.
1. Decide how many tabs you want your bottom divided into for folding purposes (See beautiful star of mesh to see how the bottom of our compost basket looked). For this photo we used 12 tabs so each tab overlapped 30 degrees (360 divided by 12).
1. Using a protractor or compass draw a circle, marking the center of the circle. Draw a line for the equator. Mark fifteen degrees north and south of the equator on both sides of the circle. Connect the marks you've made on either side of the circle to outline two 30 degree wedges.
2. Cut out one of the thirty degree wedges. The wedge should be about nine inches long.
Step 3: Cut Wire Mesh for Compost Basket
This pertains to the outer compost basket (the one made of 1/4 inch mesh to keep out rats).
1. Clip one long edge of your wire mesh rectangle every 12 inches. Cut in 12 inches. (Unless you've calculated to make wider or narrower tabs).
2. Use a sturdy straight form to help fold up the tabs you've cut. Mat used a piece of aluminum scrap and a piece of wood, but why on earth do we have nice scraps of aluminum in our garage?
Step 4: Fold Compost Basket Together
1. In order to make the bottom of the basket the tabs need to be folded so that they overlap each other by 30 degrees for our design (or whatever degrees works for the number of tabs you're using). Use the template to check that each tab is overlapping the correct amount.
2. Clip the tabs in place using 2" pieces of 12 gage mesh. First poke them through the mesh then twist them, then use pliers to bend them over themselves to create a good tight pinch.
3. Fold each following tab in to position using the template as your guide. Secure each tab as you go with a piece of wire.
4. The shape looks absolutely beautiful when the structure is completed.
Note: zip ties work great if your hands get tired of dealing with the wire.
Step 5: Make Inner Cylinder
1. The compost chamber is separated from the outer basket you just finished by a wire cylinder. Clip the cylinder together with 2" pieces of mesh.
Step 6: Put Composter Together
1. Put your finished wire mesh basket in an area that works for you.
Things to consider:
- It's going to compost much faster if it is exposed to sun and protected from the wind. We have ours on our driveway and it has no smells or flies and is currently 115 degrees on top and 135 degrees in the middle.
-The compost will leach resins from the wood or compost leachate when it rains, so you might want to have it over dirt to absorb that. We don't really care that every now and then resins from the woodchips run down our driveway, but we're inconsiderate tenants.
-It's going to be too heavy too move after you've filled it, so decide while it's empty.
2. Put the smaller cylinder of mesh inside the larger mesh basket.
4. Fill the outer ring with woodchips. Cedar takes forever to decompose. Hardwoods decompose faster. This outer ring of carbon material (wood chips in our case) will get incredibly hot as it decomposes if it is exposed to nitrogen (like urine), which is useful if you want to get your compost pile to decompose fast. 1 pound of woodchips can absorb about 3 lbs of urine easily. Urine is sterile unless it is provided by someone with kidney problems or contains blood (yuck).
5. Fill inner ring with 10" of carbon then a mixture of compost that is 30 parts carbon to 1 part nitrogen. We mix our kitchen scraps with all our household paper waste and we still have to add sawdust to get the ratio right.
6. After each addition of material to the inner ring top the compost chamber with wood chips or sawdust to keep critters from investigating the pile. We even made a mesh lid to keep critters out, but 12" of sawdust or woodchips would do the trick as well.
In this picture you can also see that we added ventilation to our last compost pile to increase bacterial activity, but that's another story you can read about on our blog where we talk about all things related to decomposing matter. In this photo there's also an inner wire mesh bin in addition to the wire fence cylinder, which proved to be a waste of time. The inner mesh bin created an air gap between the wood chips and the compost which cooled the compost down.