What's inside
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A porch planter box with a removable liner keeps wet soil away from the wood and makes seasonal changes easier. It is a manageable first woodworking project: mostly straight cuts, square corners, and screws. The key decision is what “removable” means. A fitted plastic nursery pot is easy to lift out, while a custom liner gives a cleaner fit but takes more measuring.
Contents
Choose a plan that fits your porch
This beginner plan makes a box about 24 inches long, 10 inches deep, and 10 inches tall, sized for a plastic liner roughly 22 by 8 by 8 inches. Check the liner’s outside dimensions before cutting; pots are often wider at the rim than at the base. For a longer box, add a middle support and use thicker boards to reduce bowing.
Use rot-resistant cedar or a suitable exterior-rated lumber. Cedar costs more but handles weather better than untreated pine. Pressure-treated lumber is inexpensive and durable, but avoid putting edible plants directly against it; keep soil inside a separate liner. For a first project under a covered porch, exterior-rated pine can be reasonable if it stays protected and is sealed and maintained.
Compare liner options
| Option | Best for | Trade-off |
|---|---|---|
| Plastic nursery pot or window-box insert | Fast build and easy seasonal swaps | Standard sizes may leave gaps or sit below the rim |
| Flexible pond liner or heavy-duty planter liner | Custom dimensions and a close fit | Needs careful trimming and drainage openings |
| Thin plastic sheet | Lowest-cost, covered locations | Can puncture, trap water, and deteriorate in sun |
For most beginners, a rigid plastic window-box planter liner is the least fussy choice. It supports wet soil and lifts out as one piece. A flexible flexible planter liner makes sense when the box is an unusual size, but it needs a solid bottom and protection from sharp screw tips.
Materials and tools
For a 24-inch box, buy four 1-by-6 boards, each at least 6 feet long, plus one 1-by-2 board for corner cleats. Actual 1-by-6 boards are usually about ¾ inch thick and 5½ inches wide. You’ll also need exterior screws about 1¼ and 1⅝ inches long, exterior wood finish, a tape measure, square, saw, drill-driver, and a bit for pilot holes.
A circular saw makes the cuts straightforward, but a handsaw works for this short cut list. A box of exterior-rated screws is worth buying; indoor screws can rust and stain the wood. A countersink bit is helpful but not essential. Wear eye protection, and clamp boards before cutting or drilling.
Cut list and layout
Cut the long sides into four pieces 24 inches long. Cut the ends into four pieces 8½ inches long. These dimensions make two courses of boards on each side and an interior width of about 8½ inches. Adjust the end length if your liner requires a wider box: add twice the desired change in interior width to each end piece.
Cut four corner cleats 9½ inches long from the 1-by-2. The cleats sit inside the corners, joining the side boards. Cut two bottom slats 22½ inches long, leaving a small gap between them for drainage. Dry-fit the parts around the liner before assembly. A liner that is difficult to lift out now will be worse after the wood swells.
Build the box
1. Sand cut edges and apply finish to the boards before assembly, especially the inside faces and end grain. Let the coating dry as directed. Avoid coating the removable liner unless its manufacturer says it is suitable for that finish.
2. Lay one long-side board flat. Position a cleat near each end, flush with the board’s edges, and attach it with 1¼-inch exterior screws. Drill pilot holes first to reduce splitting. Repeat for the other long side and both end boards.
3. Stand the four panels together, with the end boards between the long sides. Check that the corners are square, then fasten through the long sides into the cleats with 1⅝-inch screws. Use two screws per cleat per course, keeping them away from the board edges.
4. Set the box on a level surface. Attach the two bottom slats to the lower edges of the side and end panels, leaving a narrow drainage gap. The box is not meant to be watertight; trapped water can rot the wood and drown roots. If using a flexible liner, make drainage holes through the liner where they align with the gaps.
5. Test the liner. It should sit below the rim and lift out without catching on screws or rough edges. Round over sharp corners with sandpaper. Do not rely on a thin liner to bridge a wide unsupported gap.
Drainage, weight, and placement
Wet soil is heavy: a filled 24-inch box can weigh more than 50 pounds, depending on the mix and water content. Place it where it will stay, and confirm the porch surface can support it. Use potting mix rather than garden soil, which is heavier in containers and drains poorly. Set the box on feet or small spacers so water can escape underneath instead of sitting against the porch floor.
Drainage depends on both the liner and the box. If the liner has no holes, add several small openings according to its material and keep a tray or protected drainage area below if runoff could stain the porch. A removable liner does not prevent water damage if it overflows regularly or stays full of standing water.
Common mistakes and upkeep
The most common fit problem is measuring the liner at its narrow base rather than its widest rim. Measure length, width, and height at the points that will meet the box. Another failure is fastening close to board ends without pilot holes; this splits the wood and weakens the joint. If a board cracks, replace it rather than adding more screws into the split.
Inspect the finish each spring and touch up bare end grain. Lift the liner occasionally to clear debris and check for standing water or soft spots. In freezing climates, empty or remove the liner before hard freezes if its material may crack. With those simple checks, this plan provides an easy first build and a liner that can be swapped without dismantling the box.