Why a Timber Planter Earns Its Space

Herbs are the most-used plants in any kitchen, and the most neglected. A trip down the garden in the rain to snip a sprig of thyme rarely happens. A planter set against the back wall, a few steps from the door, changes that entirely. You brush past it on the way in, pinch off what you need, and the plants get picked regularly — which is exactly what keeps them bushy and productive.

A good size for a small workshop project is 900mm long, 300mm wide and 250mm deep. That depth suits almost everything from parsley to rosemary, holds enough compost to buffer a hot weekend, and is light enough to shift with one person when empty. Anything shallower dries out too fast; anything deeper becomes heavy and wasteful of compost.

Choosing Timber That Will Last

The single biggest mistake with outdoor planters is using whatever softwood is lying around. Untreated pine will be soft and grey within two seasons, and the joints will start to open. Choose a species with natural resistance instead.

• Oak or sweet chestnut — the traditional choices, hard-wearing and handsome, though heavy and harder to cut.
• Larch, Douglas fir or western red cedar — lighter, easier to work, and reliably rot-resistant without chemical treatment. Cedar smells wonderful in the workshop.
• Pressure-treated softwood — the budget option. Modern treatments are safe for growing, but let the timber weather for a few weeks before planting, and line the box so roots are not in direct contact.

Aim for boards around 20–25mm thick. Thinner than that and the sides will bow once the compost is wet. Use stainless steel or galvanised screws — ordinary steel will rust and stain the wood within a year. Avoid chipboard, MDF and any reclaimed timber you cannot identify; old pallet wood stamped HT has been heat-treated and is fine, but anything marked with chemical codes is not worth the risk around edible plants.

The Cutting List and Basic Assembly

For a 900 × 300 × 250mm box built from 150mm-wide boards, two courses high, you will need:

• Four side boards at 900mm (long sides, two courses)
• Four end boards at 300mm (short sides, two courses)
• Two base boards at 900 × 150mm, or one sheet cut to 900 × 300mm
• Two feet at 40 × 40 × 300mm

Butt joints are perfectly adequate here. Clamp each corner, drill pilot holes slightly smaller than your screw shank, countersink, and drive two screws per joint — offset them so the second screw does not split the grain along the first. Work on a flat surface and check the box for square by measuring both diagonals; they should match within a couple of millimetres. Fix the feet across the underside so the base sits clear of the ground, which stops damp creeping up and lets air circulate.

Drainage and Lining — the Bits That Matter Most

Herbs die from wet roots far more often than from drought. Drill 8–10mm holes at 100–150mm centres across the base before you assemble anything; it is far easier on a flat board than inside a finished box.

Line the inside with a breathable membrane — landscape fabric or hessian are ideal. This holds the compost in while letting water drain freely. Do not be tempted to use plastic sheeting or a bin liner; that turns the planter into a bath and guarantees root rot. Skip the old-fashioned layer of gravel at the bottom, too — it creates a saturated zone just above it. Mix coarse grit through the compost instead.

Filling and Planting

Use a free-draining mix: roughly two parts peat-free multipurpose, one part loam-based compost, one part horticultural grit. Mediterranean herbs — rosemary, thyme, sage, oregano, winter savory — want it leaner and grittier still, so add an extra handful of grit for their end of the box.

Space plants about 150–200mm apart and leave the tallest growers, such as rosemary, at the back. Sink a pot of mint into the compost rather than planting it directly; it spreads underground and will otherwise colonise the whole planter. Once planted, water in well and top with a 20mm layer of gravel. That keeps foliage clean and dry, and makes life harder for slugs.

Position, Watering and Yearly Care

Site the planter in full sun — six hours or more — and out of the worst of the wind, which dries leaves and snaps brittle stems. Water deeply but less often, letting the surface dry between soakings. In a heatwave you may need to water daily, and a planter against a south-facing wall will dry faster than one in the open.

Feed sparingly. A weak liquid seaweed feed every three or four weeks suits parsley, chives and basil; the Mediterranean herbs need almost nothing and will lose their flavour if pampered. Harvest little and often, cutting stems back to a pair of leaves to encourage fresh growth. Each spring, top up the compost, tighten any loose screws, and rub the outside with linseed oil to keep the timber fed. Built well, a planter like this will outlast most of the herbs you put in it.