What's inside
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A wooden planter looks simple, but soil and water are hard on lumber. The most reliable design is a decorative wood shell built around a separate plastic liner. The liner holds wet soil, while the wood stays mostly dry and can be repaired or refinished without disturbing the plants.
Contents
Project overview
This plan makes a rectangular planter about 36 inches long, 14 inches wide, and 16 inches tall. It is a manageable weekend project for a beginner with a saw and drill. The finished planter is suitable for a patio, porch, or balcony, but check the surface and weight limit first. Wet soil can weigh more than 150 pounds in a planter this size.
| Material | Advantages | Drawbacks |
|---|---|---|
| Cedar | Light, rot-resistant, easy to cut | Soft and relatively expensive; dents easily |
| Pressure-treated lumber | Inexpensive and durable outdoors | Often wet, heavy, and prone to twisting as it dries |
| Exterior plywood with trim | Stable and economical for large panels | Edges must be sealed; delamination is possible if water gets in |
For most first builds, cedar is the easiest choice. Use ordinary construction lumber only if you are willing to seal it carefully and accept more movement. A self-contained liner is still useful with either material because it prevents constant contact between damp soil and the wood.
Materials and tools
Buy two 8-foot cedar 1×6 boards for the long sides, one 8-foot 1×6 for the short sides and trim, and one 1×2 board for the top rim. Actual 1×6 dimensions are about 5-1/2 inches wide, so use three courses to create a box roughly 16-1/2 inches tall. You will also need 1-1/4-inch exterior screws, exterior wood glue, sandpaper, and an outdoor finish.
For the liner, choose a rigid plastic planter, galvanized-metal trough, or heavy-duty nursery tray measuring approximately 34 by 12 by 12 inches. Measure the liner before cutting the wood. Do not assume a container sold as a “36-inch planter” is actually that size. A liner that is too large will split the wood joints or leave the rim unsupported.
Useful tools include a tape measure, combination square, pencil, drill, countersink bit, and a circular saw or miter saw. A box of exterior wood screws is a better choice than drywall screws, which rust and snap outdoors.
Cut list and preparation
Cut six long boards at 36 inches and six end boards at 14 inches. These dimensions produce an outside length of about 36 inches and an outside width of about 14 inches when the ends fit between the long boards. Cut four rim pieces: two at 36 inches and two at about 14 inches, then trim them to fit after the box is assembled.
Dry-fit the liner between the boards before fastening anything. Leave at least 1/4 inch of clearance on each side so the liner can be removed. If the liner has a rolled lip, make sure that lip will sit below or level with the finished rim rather than being trapped under it.
Sand the board faces with 120-grit paper and ease every exposed corner with a few passes. Sharp corners shed finish quickly and are more likely to splinter. Apply a coat of exterior finish to the inside faces and cut ends now, before assembly. End grain absorbs water faster than the board faces.
Assemble the wooden shell
Start with the bottom course. Position two long boards parallel to each other and place an end board between them. Check that the corners are square, then drill two pilot holes through each long board into the end grain. Drive the screws with the heads slightly below the surface. Add the opposite end, measure the diagonals, and adjust until they match.
Do not depend on glue alone at the end-grain joints. Glue adds some stiffness, but screws provide the clamping force and remain important as the wood moves. Use a thin bead of exterior wood glue on each joint; wipe away squeeze-out immediately.
Stack the second and third courses with the end joints offset from the course below. This staggered layout is stronger and looks cleaner. Clamp or temporarily tack each board in position, then pilot-drill and screw it to the course below. Two screws near each end are sufficient for 1×6 boards. Keep the screw line at least 3/4 inch from an edge to reduce splitting.
Support the liner correctly
A plastic liner full of soil must not hang from its rim. Install three or four short cleats inside the box, about 1 inch below the top edge, so the liner’s lip rests on them. Use 1×2 scraps or treated strips, and fasten them with exterior screws from the outside if possible. If the liner has a flat bottom, add two runners beneath it to create a small air gap and prevent water from being trapped against the wood.
The liner needs drainage holes. If it has none, drill several 1/2-inch holes in the bottom, then place it where water can drain freely. Do not put a solid plastic liner directly on a porch with no drainage plan. Standing water can stain concrete, damage decking, and drown plant roots.
A rigid liner is usually the best buy because it holds its shape and can be lifted out. A heavy-duty rectangular planter liner costs more than plastic sheeting but avoids wrinkles, punctures, and unsupported soil pressure. Plastic sheeting is acceptable for a temporary or very large planter, but it needs a plywood or slatted support box and is easier to damage.
Add the rim and finish
Install the four 1×2 rim pieces around the top, keeping their outside edges flush with the box. Predrill every hole because narrow trim splits easily. A rim hides the liner edge, stiffens the box, and provides a comfortable surface to lift the planter.
Apply two thin coats of an exterior penetrating oil or water-based outdoor finish, allowing the first coat to dry fully. A clear exterior wood finish preserves the color for a while, but it will not make cedar maintenance-free. Paint offers better UV protection, while a penetrating finish is easier to refresh without scraping.
Keep the liner removable. Never caulk it permanently into the wood. At the end of the season, empty the soil, lift out the liner, rinse it, and let the wooden shell dry. Inspect the bottom edges and screw holes each spring. Touch up finish where the wood has gone gray, cracked, or started to soften.
Planting and seasonal use
Use a quality container mix rather than garden soil, which compacts and becomes heavy. Fill the liner to within 1 inch of the rim, leaving room for watering. Add a layer of mulch to slow evaporation, but do not cover the liner’s drainage holes.
In spring, check for freeze damage before planting. Frozen water expands in cracks and can split a rigid liner or swell the wood shell. In hot summer weather, inspect the planter daily; a 12-inch-deep container can dry quickly in full sun. In winter, move the planter under cover if practical, or empty it in regions with repeated hard freezes. The removable liner is the feature that makes this maintenance possible.