A cedar planter box is a straightforward weekend project that combines cedar fence pickets, corner posts, and exterior fasteners into a durable outdoor container for flowers, vegetables, or herbs.
For the full breakdown, see our best Elevated Cedar Planter Box guide.
Building your own cedar planter box costs less than buying a pre-made one and lets you control the exact size and finish. Cedar is naturally rot-resistant and aromatic, making it the top choice for outdoor planters that will live through several seasons. The basic method works the same whether you want a 12-inch herb box or a 48-inch raised bed — cut, pre-drill, assemble square, and set it in its final spot.
Materials and Tools for a Cedar Planter
The standard cedar planter uses fence pickets for the sides and 2×2 or 4×4 posts for the corner legs. Plan on about 9 pickets and 4 posts for a medium box roughly 36 inches long by 18 inches wide. You will also need exterior-grade deck screws (2 1/2-inch and 1 1/4-inch), exterior wood glue, a saw, a drill with countersink bits, a framing square, and a tape measure.
Skip interior glue entirely — Lee Valley’s plans emphasize that exterior glue is mandatory for outdoor longevity. For the frame, This Old House recommends 5/4 x 6 cedar boards with a 1-inch overhang on all sides for a clean top edge.
Related: Our tested roundup of the best elevated cedar planter box designs can help you compare pre-built options if you decide to skip the build.
Step-by-Step Build Instructions
Cut and Prep the Parts
Start by cutting your corner posts to height — a 36-inch-tall planter uses 42-inch posts if you want the box itself 30 inches tall plus 12-inch legs. Cut your cedar pickets to length for the side slats.
Assemble the Side Panels
Lay two posts flat and attach the pickets across them. Pre-drill every hole near the board edges to prevent splitting. Drive the screws until snug but stop before the head sinks into the wood — over-tightening will split cedar, especially thinner fence pickets. Use a framing square to keep the assembly square as you work. Build two identical side panels, then connect them with the end pickets to form a box.
Add the Base and Mount in Place
Attach these with 2 1/2-inch deck screws driven through the base pieces into the side panels. If your planter is larger than about 3 feet long, assemble it in its final location — the finished box is heavy and awkward to move once the base goes on. This Old House’s guide explicitly recommends building on-site.
Finishing Tips and Common Mistakes
If you plan to grow vegetables, apply exterior finish or spar urethane only to the outside surfaces so the finish never contacts the soil. For ornamental planters, a full exterior coat adds years of life. One common error is skipping the pre-drill step on cedar — the wood splits easily near ends, and a split slat weakens the whole box. Another is misaligning the posts or pickets, leaving an uneven overhang that looks sloppy and can trap moisture. Countersink screws just below the surface to avoid rust streaks over time.
Check your corners with a framing square after every few screws. A box that starts crooked will stay crooked, and it is much harder to fix after the glue sets than to catch early.
| Component | Material Suggestion | Key Assembly Tip |
|---|---|---|
| Corner posts | 2×2 or 4×4 cedar | Cut 12–18 inches taller than box height for legs |
| Side slats | Cedar fence pickets (5.5 in wide) | Pre-drill ends to avoid splits |
| Top frame | 5/4 x 6 cedar boards | Allow 1-inch overhang on all sides |
| Base crosspieces | 2×4 cedar or pressure-treated pine | Space evenly; use exterior glue and screws |
| Fasteners | Exterior deck screws (2.5 in, 1.25 in) | Do not over-drive — stop when snug |
| Finish (option) | Spar urethane or outdoor paint | Exterior only for edible plants; full coat for ornamentals |
FAQs
How long will a cedar planter box last outdoors?
Do I need to line a cedar planter box with plastic?
Lining is optional but recommended for planters holding soil directly: use a non-toxic landscape fabric or coconut coir liner to keep soil from washing out through gaps between slats while still draining. Plastic liners are not needed unless you want to hold moisture in a sealed planter box.
Can I build a cedar planter box without power tools?
Yes, but it will require more work. A handsaw and hand drill with a countersink bit can handle cedar fence pickets and 2×2 posts. Pre-drilling by hand is slower but still prevents splitting. You will also need a square and a level to ensure the box stays straight without a power miter saw.
References & Sources
- This Old House. “How to Build a Cedar Planter Box” Covers 5/4 x 6 top frame, base crosspiece placement, and on-site assembly recommendation.
- Lee Valley Tools. “Make a Versatile Cedar Planter Box” Details 45° joints, exterior glue requirement, and cedar-dust paste for filling pin holes.