What's inside
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A divided wooden seed tray keeps different crops in separate blocks, making it easier to label, move and water seedlings. This simple design has six compartments, each about 3½ by 3½ inches inside. It suits a beginner with a saw and drill, and takes roughly two to three hours to build, not counting glue drying.
Contents
Plan and materials
The tray is a shallow frame with a solid bottom and removable dividers. Removable partitions are easier to clean and let you change compartment sizes later. The tray is not watertight: use it to hold pots or a separate waterproof insert, rather than filling it directly with wet compost.
Use untreated, straight-grained lumber. Cedar resists rot but costs more; ordinary untreated pine is a reasonable budget choice if you keep the tray under cover and let it dry between uses. Avoid pressure-treated wood, painted offcuts and lumber with an unknown finish around seedlings.
- One 1-by-4-inch board, at least 48 inches long, for the sides and end pieces
- One piece of ¼-inch exterior-grade plywood, about 12 by 13 inches, for the bottom
- Two ¼-by-3½-inch divider strips, each about 11 inches long
- Four 1¼-inch exterior screws, wood glue rated for exterior use, and optional small brads
- Sandpaper, a square, tape measure, pencil, drill and saw
A bundle of untreated cedar boards is a useful upgrade if the tray will live outdoors. For an indoor or sheltered tray, pine is usually good enough.
Dimensions and cut list
Cut two long sides to 12 inches and two end pieces to 10 inches. With the end pieces fitted between the sides, the outside footprint is 12 by 11½ inches, and the inside space is about 10½ by 10 inches. The plywood bottom should be cut to match the outside footprint; check the assembled frame before cutting because actual board widths vary.
For six roughly equal compartments, make two dividers that span the inside width and one that spans the inside length. The first pair creates three rows; the second divider fits across the center row to make two smaller spaces. This layout gives four compartments of about 3½ by 3½ inches and two of about 3½ by 7 inches. Measure your actual inside dimensions and adjust divider lengths for a snug, removable fit.
Choose the bottom
| Bottom option | Best for | Trade-off |
|---|---|---|
| ¼-inch exterior plywood | A sturdy tray for pots or inserts | Can delaminate if left wet; seal the edges or dry it promptly |
| ½-inch untreated board slats | Outdoor use where drainage matters | Gaps lose compost, so use pots or a liner |
| No fixed bottom | A light frame used over a bench or flat tray | Needs support underneath and is less convenient to carry |
For this build, plywood is the simplest option. If you want a tray that holds damp material directly, a plastic insert is more reliable than trying to waterproof wood; a waterproof seed-tray insert can also make cleaning easier.
Assemble the frame
Sand the cut edges lightly so splinters do not catch on hands or fleece. Lay the two long sides parallel, then fit an end piece between them at each end. Check that the corners are square. Drill pilot holes through each side into the end grain before driving a screw into each joint; pilot holes reduce splitting, especially near board ends. Add a small amount of exterior wood glue at each joint, wipe away squeeze-out and let it cure according to the label.
Set the frame on the plywood and mark its outline. If the bottom is slightly oversized, trim it to fit rather than forcing it into place. Apply a thin bead of glue along the frame’s lower edges, place the plywood, then secure it with short brads or screws. Avoid long screws that could poke through the inside. If using screws, drill pilot holes and check the length before fastening.
Fit the dividers
Measure the inside width and cut two crosswise divider strips to that measurement. Mark three evenly spaced slots in each strip, cutting each slot halfway through the strip’s height. The slots should be just wide enough for the strip material: for a ¼-inch divider, start with a ¼-inch kerf and widen it with a file or sandpaper if needed. Test the fit on scrap first. A slot that is too loose lets the grid rack; one that is too tight can split the divider during assembly.
Slide the two slotted strips together to make a cross-shaped grid. Place the grid in the frame, then measure the center row for the final lengthwise divider. Cut matching half-depth slots in the crosswise pieces and the new divider, then interlock them. Keep the grid removable. If it shifts in use, add small corner blocks or a dab of removable putty rather than permanently gluing every partition in place.
Finish and use
Sand sharp corners and check for splinters. Leave the wood unfinished for indoor use, or apply a water-based exterior finish to the outside and let it cure fully before planting. Do not coat surfaces that will touch edible seedlings unless the finish is labeled suitable for that use. Finish slows moisture uptake but does not make plywood waterproof.
Use the compartments for pots, labels or small batches of seed-starting mix held in pots. If you fill them directly, water can pool against the plywood and swell its layers; add a fitted insert or place a waterproof tray underneath. Keep the tray level when carrying it, since the dividers are not structural and can shift under a heavy load.
Common problems and fixes
If the frame rocks, check its corners for square and sand the high corner of the bottom before adding more fasteners. If the plywood edge begins to lift, the tray has likely stayed wet; dry it thoroughly, reglue the edge if sound, and store it indoors between uses. Replace a divider that has swollen or split rather than forcing it into its slot. A quick rinse, prompt drying and a sheltered storage spot will extend the life of even a low-cost pine build.