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How to Build a Compost Bin

Composting is not only good for the planet, it’s good for the plants. It's good for the wallet, too. Here's how to build your own compost bin.

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Step 1: Select the Site for the Compost Bin

Opt for an out-of-the-way spot in your garden as the compost bin may look unsightly and unkempt at times. Avoid placing it in a shady spot where it'll take longer to "cook." The ideal location is a level, open, sunny area where the compost pile can heat up and break down at a quicker pace. Place it near a water source where a garden hose can be easily accessed since occasionally the compost pile will need to be moistened for the composting process to work.

Step 2: Cut the Lumber for the Floor Supports

The compost bin for this project has three bays and a floor. The bin provides one bay for new waste, a second bay for compost that's in the process of breaking down and the third for finished compost that's ready to use in the garden. A raised floor in this compost bin allows air circulation underneath the pile, making the gas exchange that occurs during composting more efficient.

Measure two 2" x 6" boards for the outer floor supports of the compost bin to a length of 9 feet 3 inches. Each of the three bays will be 3' wide for a sum of 9 feet. The extra 3" will cover the depth of the two end joists. Use a circular saw to make the cuts while firmly holding the boards in place on two sawhorses. These two boards will be the front and back floor supports.

Now prepare the side pieces, also known as headers. Cut two 2" x 6" lumber 30" long. To get both pieces from one board, make the first 30-inch cut, and then re-measure and cut for the second piece.

Once the outer floor supports are cut to length, cut the center joist to a length of 9 feet. This will run parallel to the two outer boards and will attach to the headers. This center joist adds stability to the floor frame and will help support the load across the floor.

Next, cut six additional floor supports from the 2" x 6" stock to a length of 14-1/2" each. These six boards, two per bay, will strengthen the floor even more.

Step 3: Assemble the Floor Supports

Lay out the frame of the floor with the two headers sitting inside the two front and back floor supports. Place the center joist and the braces within the frame. All of the braces will help the floor stay square.

Pre-drill the boards. Then screw one of the headers to each of the outer boards, using 3" galvanized screws. Attach the second header to the other end of the outer boards. Check the box to make sure it's square by measuring from corner to corner, making sure both diagonal measurements are the same.

Then screw the center joist to the headers, setting it equidistant between the two outer boards. Finally attach the six support braces to the center joist and the outer boards. Place them so that they will be directly under the center of each of the three bays.

center joist adds stability to the floor frame

Step 4: Cut the Lumber for the Floorboards

To cover the joists and headers, cut 5/4" decking boards to make 20 floorboards. Sixteen boards will be 34-1/2" long, while four boards will be 33" long, 1-1/2" shorter than the rest to leave room for the bin walls. Mark all of the boards before making the cuts. This way you can make the cuts one after the other without having to start and stop.

Lay out the four shorter floorboards in place on top of the floor supports. They must go exactly where the inner walls will go or the frame won't line up later. Measure the base to evenly divide the space into three equal areas. Two of the short boards line up even with the outside edge of the frame and the two middle boards are 37" from the outside edges.

Step 5: Assemble the Floorboards

Pre-drill the boards. Attach the two shorter outside boards with galvanized screws. Then attach the two middle short boards. Next, dry fit the remaining boards to determine the space needed between them. Remember that this floor is open to allow for air circulation underneath the compost pile, so don't worry if the boards don't completely enclose the floor. Make sure the boards are flush with the back of the bin and attach them.

Step 6: Cut the Lumber for the Posts

To start the upper frame of the compost bin, cut eight posts, 47" long, from 2" x 6" lumber. These will be the support for the outer and inner walls, four posts for the back and four for the front.

Step 7: Assemble the Posts

Place a post on each of the four corners. Then place the remaining posts to mark the inner walls of the separate bays. Screw the posts into place along the outside of the floor frame. Install them before attaching the side walls. This way you can measure the distance of the posts to make accurate cuts of the side walls.

Step 8: Build the Outer Side Walls

Measure the distance along the outside between the front and back corner supports, just above the headers on either end. Take the measurement from the bottom of the posts and use that measurement to cut all of the boards for each of the sides. By using the bottom dimension, you'll be sure to get the sides straight all the way to the top. Starting at the top of the floor, attach each outer board with galvanized screws. Leave a 1" gap between each board.

Step 9: Build the Inner Side Walls

Measure the distance between the center support posts to get the desired board lengths and then cut the pieces to fit. These can be tricky to install because you have to make sure the boards are centered in the posts. Spacing them slightly apart, attach these boards to the posts with galvanized screws.

Step 10: Build the Back Wall

Measure the back of the structure at the bottom posts and use that measurement to cut six boards, just over 9' long. These boards span all three bays because they will never have to be removed. They will attach to each of the support posts to make it sturdier.

Start by installing the bottom board, attaching it to the support posts. As you attach the back boards with galvanized screws, make sure to line up the ends of the back boards with the ends of the side walls you just installed.

Step 11: Build the Front Access Walls

The front of the compost bin is built differently because the slats need to be removable, rather than fixed like the back boards. They slide into the frame on a track. This way you can slide the slats in or out when you need to open or close the compost bins. Each compartment will have its own set of slats so they can be opened independently.

Measure the distance between the compost bin floor and the top of the side walls. Cut six pieces of 2" x 2" lumber at this length to create the tracks for the front. Since the slats that will slide between the track pieces and the front posts are one inch thick, leave a gap of 1-1/4" between the track rails so they can slide freely. Make sure each 2" x 2" track is level and attach them to the sides of the bin with galvanized screws.

Next, for each bay of the compost bin measure the distance from left to right within the tracks to get the distance you length you need to make the slats. Each bay is slightly different, so measure carefully. Cut enough 1" x 6" lumber to fit each bay.

Install the front slats on the compost bin. Like the rest of the slats, they need to have spaces between them so the air can circulate around the compost. Add screws or wood scraps as spacers between the slats.

Step 12: Fill the Compost Bin

Gather a variety of organic materials for the compost bin. Add kitchen scraps to the mix; use fruit and vegetable scraps only. Don't add meat to your compost since meat can carry harmful bacteria and attract unwanted pests to the garden. Also gather lawn debris and clippings to use for compost. Composting is a continual process and you'll need to constantly add to the pile to keep it going. For your compost to be successful, it must have a balance of 10 percent green material and 90 percent brown material for the decomposition process to begin.

One of the key ingredients in composting is water. All of your materials in your pile should be moist. You'll need to check your compost pile often and add more water if it seems to be drying out. A dry compost pile will not function properly.

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