Cut the 6-ft. boards into twenty-four 3-ft. lengths. Predrill screw holes and attach two of the 3-ft. boards to a pair of cleats with 2-in. deck screws. Square the frame by moving it until the two diagonal measurements are equal. Spread the remaining boards between the top and bottom boards so they're spaced evenly and screw them in. Repeat this procedure for the other three side panels and the back. To divide the bin into three sections, complete the back panel by screwing on two additional 2x2 cleats.
Assemble the bin by driving 2-in. deck screws through the back boards into the side panels, one screw for each board. Then drive 3-in. deck screws through the 2x2 cleats on the back panel into the 2x2 cleats on each side panel. If uneven ground makes it difficult to align the sections, place shims at the low spots.
This three-bin composter is designed to make composting tidy and effortless. It's big enough to hold most of your grass clippings, fallen leaves, pruning leftovers and the like so you don't have to haul them away. And the three-bin system speeds up the decomposition so you can return that organic fertilizer to your gardens where it'll improve the soil.
Garden waste goes into the far left bin first. After a few weeks, you move it to the middle bin (turning and aerating it in the process), where it continues to decompose. After a few more weeks, you move it to the third bin (it's ready for another turn anyway), where it's well on its way to becoming finished compost. It takes four to six weeks to make compost from start to finish, assuming you've kept the piles moist and shredded any leaves or tough stalks before adding them to the bin. Meanwhile, you've been filling the bin at the far left with fresh debris to keep the cycle going.
Stuff to avoid: Meat and bones, oils and fats, feces, seed heads, diseased plants and weed roots. In addition, if your compost turns slimy and stinks, discard it and start over. Don't use it on your plants.
Three-Bin Composter Plan
Use cedar decking (or other rot-resistant wood) to build the composter. To make a bigger composter, just use longer boards for the back.
- Six 5/4 x 6 x 10-ft. cedar deck boards (back)
- Twelve 5/4 x 6 x 6-ft. cedar deck boards (sides)
- Twelve 2x2 x 3-ft. cedar (cleats)