Build a Cedar Raised Garden Bed

Step by step How to do it

1. 01

   Cut lumber to length

   A standard 4×8 bed uses 8-foot long sides and 4-foot short sides. If your lumber comes in 8-foot lengths, the long sides need no cutting. Cut the short sides to 45 inches (not 48) to account for the corner posts — two posts at 3.5 inches each = 7 inches, so 48 − 3.5 = 44.5 inches. For a double-height bed (two boards stacked), you'll need 6 long boards and 6 short boards total. Label all pieces before assembly.

   💡 Pro tip Use a speed square to mark cutlines perfectly perpendicular. A 1-degree error on a short side becomes a visible gap at the corners.
2. 02

   Prepare the corner posts

   Cut a single 8-foot cedar 4×4 into four 12-inch pieces. These are your corner posts — they go on the inside of each corner, connecting top and bottom boards and keeping the frame square. Label them 1–4 and set aside. Check each cut with a speed square to confirm it's square on both faces.

3. 03

   Assemble the long sides first

   Lay two 8-foot boards flat on the ground, one stacked directly on top of the other. Clamp a corner post at each end, flush with the ends of the boards. The posts go on the face that will be the inside of the bed. Pre-drill two pilot holes per board-to-post connection (4 total per end), then drive 3-inch structural screws. Repeat for the second long side.

   💡 Pro tip Pre-drilling prevents cedar from splitting near the ends. Use a bit slightly thinner than your screw shank.
4. 04

   Attach the short sides

   Stand both long sides upright on their edges, corner posts facing inward, parallel to each other and 4 feet apart. Drop a short side board into position between the long sides so it butts up against the inside face of the corner posts. The short board end should sit flush with the outer face of the post. Drive two screws per board-per-post from the outside of the post into the end of the short board.

   💡 Pro tip Have a helper hold the assembly while you drive screws. The frame is wobbly until all four sides are connected.
5. 05

   Repeat for the second layer

   With the bottom course assembled, add the top course of boards. The top long boards rest on top of the bottom long boards, and the top short boards butt against the corner posts just above the bottom short boards. Drive screws through the top boards into the corner posts and (for extra strength) diagonally through the top boards into the bottom boards at each end.

   💡 Pro tip Stagger vertical screws so they don't collide inside the 1.5-inch post face.
6. 06

   Square and level the frame

   Measure diagonals corner to corner — if both diagonals are equal, the frame is square. If not, apply gentle pressure across the long diagonal to rack it into square. Clamp and recheck. Now set the frame in its final position and check level in all directions using your long level. On uneven ground, dig down slightly under the high side — a level bed drains more evenly and is easier to work with.

   💡 Pro tip Diagonal measurement is the most reliable squaring method. A square frame with "looks right" corners will warp as wood expands and contracts.
7. 07

   Lay weed barrier and cardboard

   If placing over grass, lay flattened cardboard directly on the ground inside the bed — overlap pieces by 6 inches to block light at seams. Moisten the cardboard so it makes better contact and begins composting. On top of the cardboard, roll out landscape fabric and staple to the inside of the frame boards. This combination suppresses grass for 2–3 years as the cardboard breaks down.

8. 08

   Fill with soil mix and plant

   Fill the bed to within 2 inches of the top. A good raised bed mix: 1/3 compost (homemade or bagged), 1/3 peat moss or coconut coir, 1/3 coarse perlite for drainage. This mix is lighter and more drainable than garden soil, which compacts badly in a raised bed. Water the mix before planting so it settles, then top off if needed. Plant, label rows, and water well.

   💡 Pro tip Calculate cubic feet before buying soil: length × width × depth in feet. A 4×8×1 ft bed = 32 cubic feet. You'll need 3–4 bags of each component at standard sizes, or ~30 cubic feet pre-mixed.