What's inside
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A wooden porch planter with a false bottom is a practical beginner project: it looks like a deep planter, but it uses less soil and weighs much less when moved. The raised inner floor also keeps plant roots above standing water. Build one in a weekend with straight boards, exterior screws, and a liner.
Contents
Project overview and dimensions
This plan makes a rectangular planter about 30 inches long, 12 inches wide, and 16 inches tall. The finished size can vary slightly with the actual thickness of your boards. Use 1-inch-thick cedar, redwood, or pressure-treated lumber. Cedar is easier to work with and looks better unfinished, while pressure-treated wood costs less and tolerates wet soil well.
| Material | Best use | Trade-off |
|---|---|---|
| Cedar | Visible porch planters and easier cutting | Costs more; can split near board ends |
| Pressure-treated pine | Low-cost planters exposed to constant moisture | Heavier, often damp, and less attractive unfinished |
| Exterior plywood | False bottom and hidden structural parts | Edges must be sealed; ordinary interior plywood fails quickly |
For a first build, buy two 1 x 12 x 6-foot boards for the sides and ends, plus one 1 x 8 board for the false bottom supports. Actual 1 x 12 lumber is usually about 11 1/4 inches wide, so check the boards before cutting. A box of exterior wood screws and a rectangular planter liner are worthwhile purchases; both prevent common early failures.
Simple cut list
Cut two long side boards to 30 inches and two end boards to 12 inches. The end boards fit between the long boards, producing an outside width of roughly 13 1/4 inches. If you want the planter exactly 12 inches wide, rip the long boards narrower, but that extra precision is unnecessary for a porch project.
Cut two cleats from the 1 x 8 board, each 10 inches long. These support the false bottom. Cut the false bottom from 3/4-inch exterior plywood at approximately 28 1/2 by 10 inches. Measure the assembled box before cutting this piece. It should fit inside the planter with about 1/8 inch of clearance on each side.
You will also need four short corner blocks or narrow strips of scrap wood. These are optional, but they make assembly easier and add strength at the corners. Avoid using untreated indoor screws or finish nails alone. Soil stays damp, and rusted fasteners can stain the wood or loosen within one season.
Step-by-step construction
1. Prepare the boards. Sand sharp edges with 120-grit paper. Do not sand pressure-treated lumber aggressively, and wear a dust mask when cutting any wood. Brush away loose fibers, then predrill holes near board ends. Two screws at each joint are enough for 1-inch boards, but keep the holes at least 3/4 inch from an edge.
2. Assemble the box. Stand the long boards on edge and place the end boards between them. Clamp or hold each corner flush, then drive two 1 1/4-inch exterior screws through the long board into the end grain. Check the box for square by measuring both diagonals. If both measurements match, the box is square enough. For extra durability, add a thin bead of exterior-rated construction adhesive at the joints, but do not rely on adhesive alone.
3. Install the false-bottom cleats. Measure about 5 inches up from the bottom edge inside both long sides. Mark a level line and screw one cleat to each side. The false bottom will sit on these supports. A 5-inch cavity is a useful compromise: it saves roughly 40 percent of the soil compared with filling the entire box, while leaving enough root depth for herbs, annual flowers, lettuce, and compact vegetables.
4. Fit the false bottom. Lay the plywood panel on the cleats. Drill several 3/4-inch drainage holes, spaced about 4 inches apart. Do not omit these holes. Without them, water collects in the lower cavity and adds weight, promotes rot, and can freeze and split the box. If the panel flexes, add a center support underneath it.
5. Add the liner. Set a plastic liner inside the upper planting area. A liner protects the wood, but it must not block drainage. Puncture the liner over every plywood drainage hole, or use a liner with built-in holes. If the liner stops water from reaching the holes, the planter becomes a bathtub.
6. Finish the wood. Leave cedar unfinished if you prefer a natural gray patina. For color, use an exterior penetrating oil or water-based porch-and-deck finish, applying it before adding soil. Do not coat the inside with a thick film finish that can peel and trap moisture. Allow treated wood and finishes to dry according to the label.
Soil, plants, and seasonal use
Fill the upper section with a quality container mix rather than garden soil. Garden soil compacts in a box and drains poorly. The container potting mix should contain peat or coir, compost, and perlite or another coarse material. Leave 1 inch below the rim so watering does not wash soil over the porch.
In spring and summer, use the planter for herbs, marigolds, lettuce, or compact peppers. In fall, replace heat-loving plants with pansies, kale, or ornamental grasses. In cold climates, empty the planter or move it under cover before repeated freeze-thaw cycles. Wet soil expands, and a full planter can crack at the corners or split the false bottom.
Common mistakes and useful upgrades
The most frequent mistake is building the false bottom too high. Five inches of soil depth is suitable for shallow-rooted plants, but tomatoes, woody herbs, and small shrubs need more. Lower the cleats to 3 inches from the bottom if you want roughly 8 inches of planting depth, though this uses more soil and makes the planter heavier.
Do not add gravel as a substitute for drainage. A gravel layer takes away planting depth without improving drainage above a blocked hole. Instead, use correctly sized drainage holes and elevate the planter on four rubber or plastic feet. A set of outdoor rubber feet keeps the bottom off wet porch boards and makes airflow possible.
Before filling the planter, test it with a watering can. Water should appear below the box within a few minutes. If it does not, enlarge the holes or inspect the liner. Finally, estimate the finished weight: wet container mix can weigh 20 to 30 pounds per cubic foot. Even this small planter may exceed 100 pounds when full, so build it close to its final location.