What's inside
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Building a simple outdoor trough planter is a useful summer woodworking project: it can be completed in a weekend, uses common tools, and does not require fine furniture-grade joinery. The important parts are choosing lumber that will tolerate wet soil, allowing drainage, and protecting the planter without trapping water against the wood.
Contents
Project overview and materials
This plan makes a trough approximately 36 inches long, 14 inches wide, and 12 inches tall. That size is large enough for herbs, annual flowers, salad greens, or a few compact vegetables, but still manageable when empty. Filled with wet soil, it may weigh 100 pounds or more, so build it close to its final location.
Use 1-inch-thick boards, which are actually about 3/4 inch thick after milling. You will need:
- Two side boards, 36 by 12 inches
- Two end boards, 12 by 12 inches
- One bottom board, approximately 34 1/2 by 12 inches
- Four legs or feet, each about 3 1/2 inches square and 4 to 6 inches tall
- Exterior-rated screws, preferably stainless steel or coated structural screws
- Exterior wood glue, optional but useful on protected joints
- Landscape fabric or a removable plastic liner
- Exterior finish suitable for decks, fences, or outdoor furniture
| Lumber choice | Cost | Durability | Best use |
|---|---|---|---|
| Cedar | Medium to high | Good | Longer-lasting planter with a cleaner appearance |
| Pressure-treated pine | Low to medium | Very good | Budget builds and utility planters |
| Untreated pine | Low | Poor unless well protected | Temporary planter or indoor-seasonal use |
| Redwood | Medium to high | Good | Attractive builds where locally available |
Cedar is the easiest recommendation if the price is acceptable. Pressure-treated pine is fine for a practical planter, but let freshly treated boards dry according to the supplier’s guidance before applying finish. Avoid using old salvaged lumber if you cannot identify its treatment or paint history.
Tools and summer preparation
A circular saw, drill-driver, tape measure, square, clamps, and sanding block are enough. A miter saw speeds up the cuts but is not required. Use a pack of exterior wood screws rather than general-purpose interior screws. They cost little more and are less likely to rust or snap.
Summer heat affects the work. Stack boards flat with spacers for a day or two, especially if they were stored outside. Check each board with a straightedge. A slight crown is usable; a badly twisted board will leave gaps that are difficult to close. Cut in the shade when possible, and do not apply finish to hot wood or in direct midday sun. Fast drying can leave lap marks and uneven color.
Cut and assemble the trough
Cut the side and end boards square. The exact bottom length depends on how you arrange the joints, so measure the assembled box before cutting it. With the side boards running full length and the end boards fitting between them, the bottom should be roughly 34 1/2 inches long. Dry-fit everything first.
Stand the side boards on edge and position an end board between them. Apply a thin bead of exterior glue if desired, then drill clearance holes and drive two screws through each side into the end board. Keep the screws at least 3/4 inch from board edges to reduce splitting. Repeat for the second end.
Check the box for square by measuring both diagonals. If the measurements differ, push the longer diagonal inward until they match. This is easier before adding the bottom. Clamp the box or ask someone to hold it while you fasten the bottom from underneath or through the side walls. Space screws about 6 to 8 inches apart and leave a small gap, around 1/8 inch, between bottom boards if you use more than one board.
Do not rely on glue alone. Soil stays damp, wood moves across its grain, and seasonal movement eventually breaks a glued-only joint. Screws provide the mechanical strength; glue mainly reduces rattling and small gaps.
Add drainage and keep the planter off the ground
Drill six to eight drainage holes, each 3/8 to 1/2 inch in diameter, through the bottom. Put them in two rows and keep them at least 2 inches from the edges. A common failure is drilling only one large hole or placing holes directly over a supporting leg, where water cannot escape.
Attach four feet beneath the corners, set slightly inward from the edges. Use scraps of cedar or pressure-treated stock. The feet create an air gap under the planter and protect the bottom from standing water. If the planter will sit on a deck, add rubber or plastic pads under the feet, but do not seal the entire bottom so tightly that it cannot dry.
Line the inside with landscape fabric to keep soil from washing out while allowing water through. A plastic liner can extend the planter’s life, but it must have matching drainage holes. An unpunctured liner creates a hidden water tank and rapidly promotes rot.
Sand, finish, and fill
Break sharp edges with 100- or 120-grit sandpaper. You do not need a furniture finish; sanding every surface perfectly wastes time on a planter. Concentrate on exposed corners, rough end grain, and places people will touch.
Apply two thin coats of an exterior wood stain and water repellent to the outside. Coat end grain heavily because it absorbs water faster than the board faces. Leave the inside unfinished if you are using a fabric liner, or use a finish specifically labeled for planter interiors. Do not use ordinary indoor paint on the soil-facing surfaces.
For the growing medium, use a quality container mix rather than garden soil, which becomes heavy and drains poorly in a box. Fill to about 1 inch below the rim. A thin layer of gravel is not a substitute for drainage holes; it takes away growing volume without fixing a blocked bottom.
Problems to watch for
Cracked corners usually result from screws driven too close to an edge or without pilot holes. Bowed sides come from wet, twisted boards or from tightening one screw fully before aligning the rest. Recheck square after each major assembly step.
Rot at the bottom is normally caused by poor airflow, not by a lack of finish alone. Keep the planter raised, maintain open drainage, and inspect it each spring. If the bottom feels soft, empty the planter before attempting repairs; adding more screws to rotten wood will not restore its strength.
For a cheaper build, pressure-treated pine and basic exterior screws are completely reasonable. Spend more on cedar when appearance, easier handling, and reduced chemical odor matter more than the lowest initial cost. A container potting mix and a landscape fabric roll are better places to spend money than decorative trim: they directly affect drainage and plant health.