A straightforward compost box takes a weekend to build and costs $30 to $100 in materials
A compost box is a contained space where you layer kitchen scraps and yard waste so they break down into usable compost. You can build one from untreated wood, plastic storage bins, or wire fencing—each approach takes between two and four hours and requires only basic tools. The wooden box is the most common choice for a backyard because it's sturdy, lets air flow through the sides, and you can make it any size you want.
The box itself doesn't do the composting; the microorganisms and insects in the pile do. Your job is to contain the pile, keep it moist, turn it occasionally, and add the right mix of materials. A well-built box makes all three of those tasks easier.
Key Takeaways
- A wooden compost box made from untreated 2-by-10 boards and corner posts takes about three hours to build with a drill and saw.
- The box should be at least 3 feet by 3 feet and 3 feet tall so the pile gets hot enough to break down materials quickly.
- Untreated wood, galvanized hardware, and a hinged lid or removable front panel make the box last longer and easier to use.
- You can also use plastic storage bins with drilled holes, wire fencing stapled to posts, or stacked cinder blocks instead of wood.
- Place the box on bare soil, not on concrete, so worms and beneficial insects can move in and out.
Building a wooden box: materials and tools you'll need
For a 3-by-3-foot box, buy four untreated 2-by-10 boards cut to 3 feet long, four 4-by-4 posts cut to 3 feet long, and one 2-by-10 board for the lid. Untreated wood breaks down slowly enough to last five to seven years, and it doesn't leach chemicals into your compost the way pressure-treated wood does. Avoid cedar and redwood—they resist rot so well that they also resist the microorganisms that help compost break down.
You'll also need 2.5-inch galvanized deck screws (about 24 of them), 1.5-inch galvanized screws for the lid (about 12), a galvanized hinge if you want a hinged lid, and a drill with a screwdriver bit and a 1/8-inch drill bit for pilot holes. A circular saw or hand saw, a tape measure, and a square are the only other tools required. If you don't own a saw, most lumber yards will make the cuts for you for a small fee.
Step-by-step assembly of the box frame
Lay the four corner posts on a flat surface and arrange the four boards so they form a square, with each board sitting flush against the inside of a post. Drill a pilot hole through each board into the post behind it—this keeps the wood from splitting when you drive the screw. Drive two 2.5-inch screws through each board into the post, one near the top and one near the bottom. You now have a square frame.
Stand the frame upright and check that all four corners are square by measuring diagonally from corner to corner; both measurements should be equal. If they're not, nudge the frame until they match. Once the frame is square, flip it over and screw the opposite side of each board to its post the same way, so each board is held by four screws total (two on each side).
If you want a removable front panel instead of a hinged lid, leave the front board unattached for now. You'll slide it in and out of grooves cut into the front posts, or straightforward rest it against the posts and lift it off when you need to turn the pile or harvest compost.
Adding the lid and access panel
A hinged lid lets you add materials from the top without removing anything. Cut a piece of 2-by-10 board to 3 feet long and attach it to the back of the box with a galvanized hinge, using 1.5-inch galvanized screws. The hinge should sit on top of the back board so the lid swings up and back. Add a straightforward hook-and-eye latch on the front so the lid stays closed when you're not using it.
If you prefer a removable front panel, cut a 2-by-10 board to fit the front opening and slide it into place when the box is in use. This design makes it easier to turn the pile and pull finished compost from the bottom, because you can remove the front panel entirely. Some people build a second box next to the first so they can turn the pile from one box into the other without lifting anything.
Placement and preparation of the site
Set the box on bare soil in a spot that gets partial shade—full sun can dry out the pile too fast, and deep shade slows decomposition. Make sure water can drain away from the box so it doesn't sit in a puddle after rain. If your yard slopes, place the box on the downhill side of the slope.
Before you set the box in place, clear away any grass or weeds from the footprint. You don't need to dig a hole or pour a foundation. The soil underneath lets worms, beetles, and other decomposers move in and out of the pile, which speeds up the breakdown of materials. If you place the box on concrete or a solid surface, you'll have to introduce those organisms yourself, and the pile will take longer to compost.
Alternative designs: plastic bins, wire, and cinder blocks
A plastic storage bin works well for small-scale composting. Drill 1/4-inch holes in the bottom and sides for drainage and air flow, then fill it the same way you would fill a wooden box. Bins are cheaper than wood and last longer, but they're smaller—usually 18 to 24 inches on each side—so the pile may not get hot enough to break down materials as quickly.
A wire cylinder made from chicken wire or hardware cloth stapled to four posts is the simplest design. It costs less than $20 and takes 30 minutes to build, but it offers no protection from animals and no way to contain the pile neatly. It works best in a rural setting where you don't mind a loose pile.
Cinder blocks stacked four high create a sturdy box with no tools required. Stack them in a square, leaving the holes facing outward for air flow. You can remove blocks from one side to access the pile, or build a removable wooden frame to fit inside the blocks. Cinder blocks last indefinitely but are heavy to move and harder to adjust if you want to change the size of your box.
Finishing touches and maintenance
Once the box is built and in place, line the bottom with 1/4-inch hardware cloth if you live in an area with burrowing animals like gophers or moles. Staple the cloth to the inside of the bottom boards so animals can't tunnel up into the pile. This step is optional if you don't have that problem.
Paint or stain the outside of the box if you want it to look finished, but use only exterior-grade, non-toxic finishes. The inside doesn't need treatment—it will get wet and dirty, and the finish will peel off anyway. Check the wood every year or two for soft spots or rot, especially at the corners where water collects. Replace any boards that have rotted through, and re-screw any joints that have loosened.
Frequently Asked Questions
Can I use pressure-treated wood for the compost box?
No. Pressure-treated wood contains chemicals that leach into the compost and can end up in your garden soil. Untreated wood is safer and still lasts five to seven years. If you want the box to last longer, use naturally rot-resistant wood like cedar, but be aware that it may slow decomposition slightly.
How big should the compost box be?
The minimum useful size is 3 feet by 3 feet by 3 feet. Smaller piles don't generate enough heat to break down materials quickly. Larger boxes are fine—4 by 4 feet or even 4 by 8 feet—but they're harder to turn and manage. Many people build two or three boxes so they can have one pile actively composting while another finishes.
Do I need a bottom on the compost box?
No. An open bottom lets worms and decomposers move in from the soil, which speeds up the process. If you have a rodent problem, add hardware cloth to the bottom instead. A solid bottom is not necessary and can trap water, making the pile soggy.
What if I don't have space for a wooden box?
A plastic storage bin with drilled holes works in a small space and costs $20 to $40. You can also use a wire cylinder, which takes up little room and costs even less. Both are smaller than a wooden box, so the pile breaks down more slowly, but they work fine for a household that produces a small amount of kitchen scraps.
Can I build a compost box without any tools?
Yes. Stack cinder blocks four high in a square shape and you have a box. You can also buy a pre-made plastic bin or wire bin and skip building altogether. If you want a wooden box but don't have tools, ask a lumber yard to cut the boards and a friend to help you screw them together—most people can manage that with a borrowed drill.