What's inside
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A raised herb planter is easier to work from than a bed at ground level, but a deep box full of potting mix can dry out quickly. This design adds a shallow reservoir under a slatted planting floor. Water poured into one end of the trough wicks upward through the soil, while an overflow hole prevents the reservoir from flooding the roots.
Contents
Size and design
The example below makes a planter about 48 inches long, 24 inches wide, and 32 inches high. The planting area is 8 to 10 inches deep—enough for most kitchen herbs, without making the box unnecessarily heavy. The reservoir is about 3 inches deep. Adjust the length to suit your space, but keep the width to 24 inches or less so you can reach the center from either side.
The bottom of the soil sits on a slatted false floor above a waterproof trough. A fill tube lets you water the reservoir without disturbing the soil. An overflow opening sets the maximum water level. This is a self-watering aid, not an automatic irrigation system: check moisture regularly, especially in hot weather.
Materials and tools
Use cedar or another naturally rot-resistant wood for the exposed frame. Pressure-treated lumber is a practical, cheaper choice for structural legs and rails, but avoid using freshly treated boards where they contact edible planting mix. For the trough liner, use a pond-liner or potable-water-safe liner rated for outdoor use; ordinary thin plastic can split at folds or punctures.
You’ll need 2-by-2-inch stock for legs and supports, 1-by-6-inch boards for the sides, 1-by-3-inch boards for the false floor, exterior screws, a drill, saw, square, tape measure, and staples or cap fasteners suited to the liner. A small EPDM pond liner is a straightforward liner option. A basic PVC pipe and elbow can serve as the fill tube.
| Material | Advantages | Trade-off |
|---|---|---|
| Cedar | Light, easy to cut, naturally rot resistant | Costs more and can split near board ends |
| Pressure-treated lumber | Affordable and durable for the frame | Heavier; keep it separated from the planting mix if you prefer |
| Untreated pine | Lowest initial cost and easy to find | May decay quickly where soil or water stays against it |
Cut list and preparation
For a 48-by-24-inch box, cut four legs to 32 inches. Cut two long side boards to 48 inches and two end boards to 21 inches; the end boards fit between the long sides, making the outside width about 24 inches. Cut the lower reservoir supports and upper planting-floor cleats from 2-by-2 stock. The exact cleat length depends on whether you fasten them inside the legs or between the rails, so dry-fit the frame before cutting those pieces.
Cut enough 1-by-3 slats to span the 21-inch inside width, leaving roughly 1/4-inch gaps between them. These gaps allow water to wick upward and give excess water somewhere to drain into the trough. Sand sharp corners and seal cut ends with an exterior wood finish compatible with your planting setup.
Build the frame
Assemble the two long sides first. Fasten each side board to the legs with two exterior screws at every leg, predrilling near board ends to reduce splitting. Position the end boards between the long sides and screw them to the legs. Check that the box is square by measuring both diagonals; if they differ, shift the frame until the measurements match.
Fasten a pair of 2-by-2 supports inside the frame near the bottom, about 6 inches above the ground. These hold the reservoir floor. Install another pair of cleats about 3 inches above the intended reservoir bottom to support the slatted planting floor. Use a level so water does not collect in one corner. Add a bottom panel or closely spaced boards on the lower supports to carry the liner and water. A full reservoir can weigh more than 100 pounds, so do not rely on a few screws driven into end grain.
Install the trough and watering parts
Lay the liner into the lower compartment, pressing it into the corners without stretching it tight. Leave enough material to fold up the walls by at least 4 inches above the reservoir floor. Secure the upper edge with liner-safe fasteners above the planned waterline. Keep screw tips and rough edges away from the liner; a small puncture can empty the trough overnight.
Make an overflow opening through one short end of the liner and box, about 2 inches above the reservoir floor. Fit a short sleeve or grommet if available, and seal around it with a product approved for the liner material. Test the trough with water before covering it. If it leaks, repair it and retest rather than hoping the soil will catch the leak.
Place a fill tube in one corner, extending from just above the rim down to within an inch of the reservoir floor. A 1-inch pipe is wide enough to fill without much fuss. Cut its top at an angle or add a funnel. The tube must remain accessible after the soil is added.
Add the floor and planting mix
Set the 1-by-3 slats on the upper cleats with approximately 1/4-inch gaps. Cover them with a layer of landscape fabric or fine mesh to keep soil from falling into the reservoir while still allowing moisture through. Avoid a solid plastic sheet here: it blocks the water path and can trap excess moisture against the roots.
Fill with a lightweight container mix, not dense garden soil. A simple blend is two parts potting mix to one part finished compost, with perlite mixed in if the blend feels heavy or stays soggy. Leave about an inch of headspace. Plant herbs with similar water needs together: basil and parsley tolerate more moisture than rosemary, thyme, and oregano. Keep the dry-loving herbs toward an edge where you can water them separately if needed.
Watering and maintenance
Fill the reservoir until water reaches the overflow, then wait for the surface mix to begin drying before refilling. For the first week, check moisture with a finger 2 inches down; a reservoir can be full while the upper root zone is still dry. Water from above during establishment, then use the trough as a backup supply. In hot, windy weather, a 3-inch reservoir may last only a day or two.
Common failures are a leaking liner, blocked overflow, and roots sitting continuously wet. Keep the overflow visible and clear of leaves. If the mix smells sour or herbs yellow despite damp soil, stop filling and check drainage. At the end of the growing season, empty standing water in freezing climates, clean the fill tube, and inspect the liner for wear. Replace a cracked or brittle liner before the next planting rather than patching a large failure.