DIY Two-Bin Composter
By Michelle Balz Anna Stockton | Feb 12, 2019
All serious gardeners acknowledge the undeniable benefits of compost, and most maintain their own compost-bin system. If you want to join their ranks, you’ll need a system that can handle a large volume of material and allow easy access to finished compost. Serious gardeners tend to have lots of material from plant clippings and weeds, but they also seek out compost fodder from outside sources. They grab extra coffee grounds from the local coffee shop, and happily accept bags of their neighbors’ leaves.
Having a multiple-bin system allows gardeners to move partially composted material from the first bin into the second before filling up the first bin again. This movement aerates the pile and speeds decomposition, something very important to gardeners who not only have a large amount of material to handle, but also clamor for the finished product to use in their gardens.
This wood and wire bin offers great airflow, great capacity, and a good amount of critter-proof security. I also think this type of bin looks natural in the garden. If you build it as described, you’ll have a first-rate compost bin, but you could easily adapt these plans to construct a two-bin unit from wood pallets or leftover lumber. Cedar is naturally weather- and pest-resistant, and smells amazing when you cut into it. The dimensions listed below will work great if you use grade A cedar boards or pressure-treated lumber. If, on the other hand, you choose rough-sawn cedar from a specialty lumber yard, you’ll save a considerable amount of money (it’ll be about half the cost), but the boards will come in a larger size than dimensional lumber. With a little extra math, you can make rough-sawn cedar work.
The materials list for this project may seem intimidating at first glance, but you can easily make this bin in a weekend while allowing generous time for breaks.
Tools & Materials
- 65 feet of cedar 2-by-4s
- 25 feet of cedar 2-by-2s
- 9 feet of cedar 2-by-6s
- 31 feet of cedar 1-by-6s
- 21 feet of 1/4-inch hardware cloth, 36 inches wide
- (8) 3-1/2-by-3/8-inch carriage bolts with washers and nuts
- 1-pound box of 3-1/2-inch wood decking screws
- (3) 32-by-26-inch pieces corrugated roofing
- 12 feet wiggle molding
- 40 gasketed roofing screws
- 2 hinges, galvanized or stainless
- (4) 4-inch galvanized flat corner braces
- (2) 4-inch galvanized flat T-braces
- Staple gun and staples, 3/8 inch or similar
- Drill and drill bits
- Aviation shears
- Tape measure
- 3/4-inch socket or box wrench or adjustable wrench
- Carpenter’s square
- 2 eye hooks and 8 inches chain
- Safety glasses
- Ear protection
- Wood chisel
- (6) 31-1/2-inch 2-by-4 cedar boards
- (6) 36-inch 2-by-4 cedar boards
- (4) 6-foot 2-by-4 cedar boards
- (3) 29-inch 2-by-4 cedar boards
- (4) 34-1/2-inch 2-by-2 cedar boards
- (1) 6-foot 2-by-2 cedar board
- (3) 29-inch 2-by-2 cedar boards
- (3) 36-inch 2-by-6 cedar boards
- (12) 31-inch 1-by-6 cedar boards
Build the Main Structure
1. Create three rectangular frames to form the bin’s two ends and its center divider. Make each frame by screwing together two 31-1/2-inch 2-by-4s and two 36-inch 2-by-4s with wood decking screws. Set the ends of the two 36-inch pieces on the outside of the shorter boards at the corners. If you predrill the holes before screwing, the wood will be less likely to split. Make these boxes as square as possible or your finished compost bin will be a bit wonky.
2. Wearing gloves, cut three 33-1/2-inch pieces of hardware cloth (33-1/2 by 36 inches). Cut as close to the wire intersections as possible to avoid snags. After cutting each piece, cut the orphan ends to start with a fresh edge.
3. Staple the hardware cloth to the frames. It helps to have two people, so one person can hold the cloth tight while the other operates the stapler. Starting in the middle of a board will also help keep the pieces straight. Staples are inexpensive, so you can afford to be a bit generous to make sure the mesh is secure.
4. Next, build a large rectangle with the three frames you just assembled and three of the 6-foot-long 2-by-4s. Position two of the 2-by-4s across what will be the bottom of the bin, and one 2-by-4 across what will be the upper back. (The upper front does not have a 2-by-4.) Place two of the frames at the ends, making sure the hardware cloth faces out. The third frame goes in the center. Drill a 3/8-inch hole at each intersection and install the carriage bolts to attach the frames to the 6-foot 2-by-4s. If you want to skip the carriage bolts, you could assemble the rectangle with deck screws, but carriage bolts offer a tight fit and stronger hold.
5. Turn your rectangular bin so the bottom is facing up. You can see how the 2-by-4s rest on the surface of the frames. You need to add filler blocks between the two 6-foot 2-by-4s to support the hardware cloth you’ll be stapling to the bottom. To install the filler blocks, screw 29-inch 2-by-4s onto the bottom of the frames to fill in the gaps. You can assemble the filler blocks using multiple scrap pieces if necessary.
6. Wearing gloves, cut two 6-foot pieces of hardware cloth (6 feet by 36 inches). Staple these pieces on the back and the bottom of the bin. It’s easiest to start in the middle, followed by the corners, and then fill in the areas between with staples. Add hardware cloth on the bottom, too, to block moles and other digging critters from entering your bin.
Construct the Lid
7. Assemble the lid with three 29-inch 2-by-2s for the side and center brace pieces, one 6-foot 2-by-2 for the front brace, and one 6-foot 2-by-4 for the back brace (for extra support). As with the frames in Step 1, you’ll want to set the ends of the longer boards on the outside of the shorter boards at the corners. Use the metal flat corner braces and flat T-braces. (Although you could make the lid frame entirely of 2-by-4s, it would be very heavy to lift.)
8. Using aviation shears, cut the corrugated roofing into three 32-inch pieces.
9. Leaving room on the back board for the hinge, place the wiggle molding along the front and back edges of the lid. Wiggle molding easily snaps together to form a 6-foot piece.
10. Place the roofing pieces on the wiggle molding. If your roofing has a glossy side, place that side up. Make sure each piece overlaps by about 1 inch. Drive the gasketed screws into the bottom of the divot through the wiggle molding and into the board.
11. Set the lid on the main structure and attach the hinges. Practice opening and shutting the lid to make sure you leave enough room for the hinges.
12. Attach eye hooks to the edge of the lid and the main bin. Connect with a chain to prevent the lid from falling backward.
Create the Front Slats
13. Screw three 36-inch 2-by-6 boards to the front of the frame, one at each end and one in the middle. Close the lid on the compost bin to judge where the slats should be placed.
14. To create the track into which the slats will slide, screw the four 34-1/2-inch 2-by-2s on the inside of the frame. You’ll want to leave enough room for the slat boards to easily slide up and down.
15. At this point, test the 1-by-6 slats in the track and cut off any length necessary so the boards fit easily. You may also chisel the frame to create a smoother slide. Spending a little extra time on this step now will save you frustration later when you want to turn the piles inside the bins.
Once you slide the slats into place, your bin system is complete. Start by filling one of the units with leaves, yard trimmings, and food scraps. After a few months, or when the first unit is full, slide out the slats and use a pitchfork to move everything into the second unit. This aerates the composting material. By the time you’ve filled the first unit again, you’ll probably have finished compost ready for your garden in the second.
One major factor to consider when choosing a composting technique is how you’ll keep animals, especially rodents, out of your compost pile. Rats and mice have very sharp teeth and a particularly determined mindset when it comes to accessing rotting fruits and vegetables.
Aside from burying your food scraps in leaves and using coffee grounds, you can also sprinkle cayenne pepper on top of the bin to deter rodents. Perhaps the best defense is choosing a very hardy compost bin to keep them out. If you have a rodent problem, build this two-bin unit with 1/4- to 1/2-inch wire mesh at 16- to 20-gauge strength. With strong wire and wood and a sturdy, secure lid, the bin may be more effective at deterring rats than even a plastic bin, as rats have been known to chew through plastic.
Excerpted with permission from Composting for a New Generation: Latest Techniques for the Bin and Beyond by Michelle Balz, published by Cool Springs Press. The bin was adapted from designs created by Andrew Sigal and StopWaste.
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