What's inside
As an Amazon Associate I earn from qualifying purchases. This post may contain affiliate links at no extra cost to you.
A removable liner makes a window herb box easier to plant, clean and bring indoors when the weather turns. This design uses a cedar outer box and a separate plastic nursery tray, so wet soil does not sit against the wood. It suits a beginner with a saw and drill, and takes about an afternoon to build, not counting paint or finish drying time.
Contents
Choose a size and plan for drainage
The example box measures 24 inches long, 7½ inches deep and 7 inches tall. It fits many standard window trays, but measure your liner before cutting: leave about ⅛ inch of clearance on each side so it lifts out without sticking. Check that the sill can support the weight. A watered box this size can weigh 20 pounds or more; do not rely on a narrow or loose sill.
Use a liner with drainage holes and a waterproof tray underneath, or put drainage holes in the liner if it is designed to be drilled. Water must not pool around roots, but runoff should not drip onto siding or a walkway. Never make the wood box itself the only container for wet soil.
Materials and tools
For the outer box, buy one 1-by-8 cedar board at least 6 feet long. Its actual width is usually 7¼ inches. You will also need exterior-rated screws, wood glue labeled for exterior use, sandpaper, and an appropriately sized plastic planter liner. Cedar is naturally rot resistant and easy to cut. Pine costs less, but needs a durable exterior coating and is more likely to decay if the liner leaks.
A circular saw or handsaw, drill/driver, tape measure, square and clamps are enough. A box of stainless or coated exterior screws is a sensible buy; ordinary interior screws can rust and stain the wood. A drill bit for pilot holes helps prevent cedar from splitting.
Cut list and liner options
Cut the board into two 24-inch pieces for the front and back, and two 6-inch pieces for the ends. The end pieces fit between the long boards, making the finished length about 25½ inches. Cut a ¼-inch plywood bottom to fit inside the box, approximately 24 by 6 inches; measure the assembled opening before cutting for a snug fit. The bottom supports the liner, not the soil directly.
| Choice | Advantages | Trade-off |
|---|---|---|
| Removable plastic tray | Easy to lift out, clean and replace; protects wood | Must fit closely and have drainage managed |
| Landscape fabric liner | Cheap and easy to trim | Holds moisture against wood and is not truly removable when planted |
| Wood box with drainage holes | No separate tray to size | Water wets the box and may stain or damage the sill |
For a removable setup, use a rigid tray rather than fabric. Search for a plastic window-box liner by its inside dimensions, not just its advertised length. A cheap nursery tray is fine if it does not flex when lifted with damp soil.
Assemble the wooden box
Sand the cut edges, then dry-fit the sides around the bottom. The bottom should sit flush with the lower edges of the sides. Apply a thin bead of exterior wood glue to each end joint. Drill two pilot holes through each long side into each end, then drive 1¼-inch exterior screws. Keep the box square by checking both diagonal measurements; they should be nearly equal.
Attach the plywood bottom with screws spaced about 5 inches apart. Do not glue it permanently if you may need to replace it later. If the bottom fits loosely, add a small bead of exterior sealant on the inside seam, but keep it out of the liner’s path. A removable liner should lift out without catching on screws or sharp edges.
Test the fit with the empty liner. If it binds, sand the inside edges or trim the liner only if its manufacturer allows it. Add two small wood cleats inside the ends if the tray needs support; position them so the tray rim remains accessible to grip.
Finish the wood and manage water
Round sharp corners lightly and sand to 120 grit. Apply two thin coats of exterior paint or a plant-safe exterior finish to the outside and exposed inside surfaces, following the label’s cure time before planting. A low-odor exterior wood sealer is useful if you want to keep the grain visible, but no coating makes a leaking liner harmless. Let the finish cure fully; a box that still smells strongly of solvent is not ready for herbs.
Set the box on the sill only after confirming it sits flat. Use a shallow waterproof saucer beneath the liner if the tray has drainage holes, and empty it after watering. Do not block weep holes in the window frame. If the sill slopes, use a stable, non-absorbent shim under the box rather than wedging it against the glass.
Planting and seasonal care
Put a thin layer of potting mix in the liner, arrange herbs with room for mature growth, then fill around the roots. A 24-inch box can hold three or four compact herbs; crowding five or six may look full at first but encourages weak growth and makes watering uneven. Choose plants with similar light and water needs. Basil prefers more moisture than rosemary, for example, so they are easier to manage in separate liners.
Lift the liner by its rim, not by pulling on the wood. At the end of the season, empty and wash it, dry the wooden box, and store the tray separately if freezing weather is expected. Check screw joints and the finish each spring. If the wood stays damp, paint bubbles, or the bottom softens, fix the leak before using the box again.