Single bin compost bin plans

Parts

Cut list

Kerf 1/8″ included. Every cut runs edge to edge.

Steps

• Tape measure
• Speed square
• Pencil
• Drill/driver
• Clamps
• Safety glasses
• Hearing protection
• Dust mask
• Circular saw or miter saw
• Miter saw, or circular saw in two passes, for 4×4 posts
• Post-hole digger
• Hand tamper
• 4′ level
• Tin snips and leather gloves
• Sander, 120 and 180 grit

Underlined words have a short explanation: hover or tap them. All of them are on the glossary page.

1. 1Before you start

   Read every step once, start to finish, before you buy or cut anything. Each step names the parts it uses by letter; the parts list gives their sizes.

   Set up somewhere flat with good light. A pair of sawhorses with a sheet of plywood on top makes a fine work table.

   Wear safety glasses whenever a tool is running, hearing protection for saws, and a dust mask for sanding and for cutting treated wood or sheet goods. Tie back long hair and loose sleeves. Keep children and pets out of the work area.

   • Tip At the store, pick straight boards: hold each one up to your eye and look down its length. Skip boards that bow, twist or have big knots near the ends.
   • Tip Measure twice, cut once. Most mistakes are a misread tape, not a bad cut.

2. 2Cut and label the parts

   Cut every part on the cut list. Cut the longest parts first: if one goes wrong, it can still become a shorter part.

   To mark a cut, hook your tape on the end of the board, make a small V with its point exactly at the measurement, and draw a square line through the point with a speed square. Put an X on the waste side.

   Cut on the waste side of the line, so the blade's kerf (about 1/8″) comes out of the scrap, not your part.

   Write each part's letter in pencil on a face that won't show, and stack the parts by letter.

   Sand the faces before assembly while they're flat and easy to reach: 120 grit, then 180.

   ✓ Lay the parts out and count them against the parts list. Measure a few: if one is off by more than 1/16″, recut it now.

   STOP. Let the saw reach full speed before it touches the wood, keep both hands clear of the blade's path, and never reach under a board you're cutting. Support long boards on both sides of the cut so the blade doesn't pinch.

3. 3Pick the boards and the screws

   Cedar for the compost bin: look for boards with mostly reddish-brown heartwood. Pale yellow-white streaks are sapwood, which rots years sooner; keep those streaks on the inside or skip the board.

   Pressure-treated pine: read the end tag. Parts that touch soil, sit in wet mulch or go in the ground must say "ground contact"; "above ground" lumber is fine for everything else. New treated boards are often wet and heavy: stack them flat with scrap sticks between them for a week or two in the shade so they dry and stop twisting.

   Sight down each board at the store like a rifle barrel. Skip boards that twist, bow more than about 1/4″ over 8′, or have big loose knots near where you will cut or screw.

   Use exterior screws only: coated deck screws (labelled for treated lumber, "ACQ compatible") or stainless steel. The copper in treated wood eats plain and zinc-plated steel within a few years. Indoor wood screws and drywall screws rust and snap outdoors.

   Compost is made by the same fungi and bacteria that rot wood, so a bin lives a hard life. The posts are always ground-contact pressure-treated. For the boards, cedar lasts 5–10 years against compost; pressure-treated 5/4 deck boards last longer and are stiffer.

   Modern treated wood (labelled CA or ACQ) leaches a little copper near the boards. Most gardeners don't mind; if you will grow food in the compost and want none at all, choose cedar.

   • Tip Buy one extra board of the most-used size. A split or a mis-cut then costs you nothing but a few dollars.
   • Tip Cedar splits easily: predrill every screw within 2″ of the end of a board with a bit about the size of the screw's inner shank.

   ✓ Every board is reasonably straight, and the screw box says exterior, coated for treated lumber, or stainless.

4. 4Call 811 and check the spot

   At least 3 working days before you dig, call 811 (or use call811.com). It's free. They send people to paint or flag buried gas, electric, water and cable lines near where the compost bin will go.

   Check your property line on your survey or plot plan, and ask your town about setbacks, easements and whether this needs a permit.

   Pick ground that drains: not a low spot where puddles sit after rain, and not over a septic field.

   STOP. Don't dig until the marks are down. Hitting a gas or power line can kill you and is expensive to repair.

5. 5Mark out a square rectangle

   Hammer a stake at one corner of the compost bin (outside faces of the posts). Measure 43″ along the long side and hammer a second stake. Tie mason's line tight between them, a few inches off the ground.

   For the first square corner, use the 3-4-5 rule: from the first stake, mark 3 ft along the string. Run a tape 4 ft out roughly at 90°. Swing it until the 3 ft mark and the 4 ft point are exactly 5 ft apart. That direction is square: set a stake 36″ out along it.

   Measure the last corner from the other two (43″ and 36″) and set the fourth stake. Run string around all four.

   Measure both diagonals, corner to corner. Nudge the stakes until the two numbers match.

   • Tip For bigger layouts use 6-8-10 instead of 3-4-5: the bigger the triangle, the more exact the corner.
   • Tip Batter boards (two stakes with a crosspiece set 2 ft outside each corner) let you take the strings down to dig and put them back in exactly the same place.

   ✓ Sides are 43″ and 36″ and the diagonals match within 1/2″. Spray marking paint along the strings, then pull the stakes you're about to dig around.

6. 6Mark the post centres

   The string rectangle is the outside of the posts. Along the back string, mark 2 post centres: the first 1 3/4″ in from the corner, then every 39 1/2″. Do the same along the front string.

   Spray a dot of marking paint at each mark and take the strings down to dig (leave the stakes in to put them back).

   ✓ Front and back marks line up across the bin; 32 1/2″ from each back mark to its front mark.

7. 7Set the posts in gravel

   Dig 4 holes about 10″ wide and 12″ deep with a post-hole digger.

   Pour 3″ of gravel in each hole and tamp it hard with the end of a 2×4. This lets water drain away from the post end.

   Stand a post in each hole. Put the strings back up at the post outside faces, and run one more string across the post tops 36″ above the ground to set their height; dig a little deeper or add gravel under a post until its top meets the string.

   Hold the post plumb with a level on two faces and fill around it with gravel 3″ at a time, tamping each layer hard all the way round before the next. Packed crushed gravel locks the post almost as well as concrete for a low bin and lets water drain.

   • Tip Use crushed gravel with sharp edges (3/4″ crushed stone), not round pea gravel: round stones roll and never lock.

   ✓ Every post is plumb on two faces, its outside face touches the string, and you can't wiggle it by hand.

8. 8Screw on the back wall

   Start at the top: screw the first back slat (B) across the back faces of the back posts, its top edge flush with the post tops.

   Work down, leaving a 1″ gap between slats (a scrap of 1×2 laid on edge is close; or cut a 1″ spacer): 5 rows. The bottom one ends about 4 1/2″ above the ground.

   Two 1 5/8″ exterior screws into each post, predrilled near board ends.

   • Tip The gaps let air into the pile. Compost without air goes slimy and smells; with air it smells like a forest floor.

   ✓ The gaps are even and the slats are level; sight along them from one end.

9. 9Screw on the end walls

   Screw the end slats (C) to the outside faces of the two end posts, the same way and at the same heights as the back. Each runs the full 36 3/4″ from the back of the back slats to the front of the front post.

   ✓ The end slats line up with the back slats at every corner.

10. 10Make the channels for the front boards

    The front boards slide down into slots on the front posts so you can lift them out one by one: to reach in and turn the pile, and to shovel out finished compost from the bottom.

    In each bay, on both front posts, screw a channel cleat (D) upright against the inside face of the post, flush with its back face. Then screw a front stop (E) flush with the post's front face. That leaves a 1 1/4″ slot between them.

    Drive four screws per piece: 3″ for the cleats, 1 5/8″ for the stops, predrilled.

    • Tip Hold a scrap of front board in the slot while you screw the stop on; it sets the gap for you. Then slide the scrap out.

    ✓ A scrap of the front board slides down every slot without binding, and the slots on both sides of a bay are the same 36″ apart.

11. 11Fit the front boards

    Cut 6 front boards (F) per bay, 35 3/4″ long: 1/4″ short so they drop in easily even when swollen with rain.

    Round the ends slightly with sandpaper or a rasp so they don't catch, and number each one on the end (bay, row) with a paint pen.

    Drop them into the slots, stacked tight.

    ✓ Each board lifts out with one hand and drops back without forcing.

12. 12Lay the wire floor

    Cut hardware cloth for each bay 48″ × 41″: 6″ bigger than the floor on every side. Cut it with tin snips and wear leather gloves; the cut ends are sharp.

    Lay it flat on the ground inside the bay, bend the 6″ border up against the walls, and screw it to the inside of the lowest slats every 6″ with the washer-head screws. Staple between screws.

    At the front, leave the wire flat on the ground under the front boards, so you can still shovel out the bottom.

    ✓ There is no gap at the edges wider than a finger where a rat could push through.

    STOP. Wear gloves and eye protection when cutting and bending hardware cloth: it springs back.

13. 13Protect it from the weather

    Decide how you want the compost bin to look in five years. Bare cedar and bare pressure-treated wood both weather to silver-grey and still last many years; doing nothing is a real option.

    To keep the colour, use an exterior oil or semi-transparent stain: brush it on, let it soak in 15 minutes, then wipe off whatever is still shiny. Renew it every one or two years. Avoid clear varnish or polyurethane outdoors: sun cracks the film, water gets under it, and it peels.

    Pressure-treated wood must dry before any stain or paint. Sprinkle a few drops of water on it: if they bead up, wait; if they soak in within ten minutes, it is ready. This can take a few weeks to a few months.

    • Tip Finish on a dry day above 50°F with no rain forecast for 24 hours.
    • Tip Oil-soaked rags can catch fire on their own as they dry. Lay them flat outside to dry or keep them in a sealed metal can of water.

    ✓ The finish is dry to the touch everywhere, with no wet or shiny puddles in corners.

14. 14Start the pile

    A hot pile needs four things: greens (kitchen scraps, grass clippings), browns (dry leaves, straw, shredded cardboard), air, and water.

    Layer about two buckets of browns for every bucket of greens, a few inches at a time, and sprinkle each layer with a hose. It should feel like a wrung-out sponge.

    No meat, fish, dairy, oil, pet waste or diseased plants: they smell, draw animals, or spread disease.

    Turn the pile every two or three weeks: lift out the front boards and fork it into the next bay, or out and back in. Each turn lets air in and heats it up again.

    • Tip Too wet and smelly: add browns and turn it. Dry and not heating: add greens and water.

    ✓ A week after building a full pile, the middle feels warm to a hand pushed inside. It's done when it's dark, crumbly and smells like soil.

15. 15Finish

    Ease every sharp edge and corner with 120-grit sandpaper so nobody gets a splinter.

    Sand all over with 180 grit, always along the grain (the direction the wood fibres run). Scratches across the grain show through stain.

    Wipe off the dust with a barely damp rag and let it dry.

    Outdoors, use an exterior finish: a penetrating deck oil or exterior stain, or primer and exterior paint. Leave cedar bare to weather silver if you like. If it holds soil for food plants, leave the inside unfinished.

    Let it dry for the time on the can before using it.

    • Tip Try your finish on a scrap of the same wood first: stain looks different on every board.