Why a Pallet Planter Earns Its Place By the Back Door

A standard pallet measures roughly 1200mm by 1000mm, which is about the footprint of two paving slabs — small enough to sit against a wall on the narrowest patio, but tall enough to give you somewhere in the region of a dozen planting pockets. That matters on a British patio, where floor space is precious and the wall above it is doing nothing at all. Stand the pallet on its long edge and you get a living wall of herbs, at picking height, a couple of steps from the kitchen sink. Thyme for a roast, mint for a jug of water, parsley to chop over new potatoes — all within reach, and all within about £20 if you source the pallet free.

Choosing a Pallet Worth Planting In

Not every pallet is a good idea. Take a minute before you load one into the car.

• Look for the HT stamp. Heat-treated timber is marked HT and is the safe choice for anything growing food. Avoid anything stamped MB, which has been fumigated with methyl bromide.
• Inspect for contamination. Reject pallets with oil stains, blue-green mould, chemical smells or spills you cannot identify.
• Check the structure. You want dry, sound boards with no rot and no deep splits. Softwood pallets are lighter and far easier to cut than hardwood.
• Avoid broken deck boards. Every board you lose is a shallow pocket that will dry out and shed compost.

Ask at a builder's merchant, a tile shop or a garden centre — they usually have a stack by the yard and are happy for it to go. Never take one from behind a shop without asking, and never use one that has clearly been sitting in the rain for a year.

Turning the Pallet Into a Vertical Planter

The simplest and strongest approach is to keep the pallet whole and stand it upright on one of its long edges, so the three stringers run vertically. You now have three deep channels, each with slatted deck boards forming a front face and a back face.

Lay the pallet flat first and work on it before it goes vertical. Wrap the back face and the bottom of each channel with a breathable membrane — a woven weed-suppressing fabric is ideal, and a couple of metres will do the whole job. Staple it firmly along the back, down the sides and across the base of every channel. The membrane holds compost in while letting water drain away. Do not be tempted by plastic sheeting; it traps water, sours the compost and rots the timber.

At the bottom of each channel, wedge a spare deck board or a strip of timber across to act as a retaining lip, then staple membrane over it. This stops your compost washing out through the lowest gap the first time you water properly. Finally, sand any rough edges with 80-grit paper, then 120, so you are not catching your forearms every time you reach for the parsley.

Place the pallet where it will live before you fill it. Once loaded, it will weigh 100kg or more and will not move. A south- or west-facing wall is ideal. Lean it against the wall and secure it with an angle bracket into the masonry, or strap it to a fence post — a tall, top-heavy pallet will go over in a winter gale.

Filling the Pockets and Planting Your Herbs

Fill each channel with multi-purpose compost firmed in gently, working from the bottom up so you do not end up with hollow pockets halfway down. Mix roughly one part horticultural grit to four parts compost for thyme, rosemary and oregano; they hate sitting wet. For parsley, mint and chives, straight multi-purpose is fine.

Plant into the gaps between the deck boards, easing the roots through with your fingers and firming the compost around them. A few specifics worth knowing:

• Mint spreads by runners and will bully everything else in the pallet. Sink a 2-litre pot of mint into its own pocket, rim just above compost level, so the roots stay contained.
• Thyme wants the driest, sunniest pocket near the top and a gritty mix. It sulks in rich, damp compost.
• Parsley likes fertile, moist soil and a little shade in the afternoon. Flat-leaved types crop harder than curly ones.
• Basil is frost-tender. Treat it as a summer guest and expect to replace it each May.

Space plants 15–20cm apart, and leave the topmost pockets for trailing thyme or nasturtium, which will soften the whole thing as it grows.

Watering, Feeding and Keeping It Going

Shallow pockets dry out fast, especially against a warm wall. From May to September, water every morning at the base rather than over the leaves — a watering can with a fine rose, or a length of soaker hose clipped along the top channel, both work well. Stirring a handful of water-retaining granules into the compost at planting time buys you a day's grace on a hot weekend.

Feed with a liquid seaweed or tomato feed every fortnight through the growing season; herbs cropped hard in a confined pocket soon run out of puff. Trim mint and parsley regularly to stop them bolting, and pinch out thyme tips to keep it bushy. Slugs will find the lower pockets — a beer trap or a nightly torchlight patrol sorts most of it.

Come autumn, cut mint back hard and it will return next spring. Thyme and chives are hardy and need nothing more than a top-up of compost in March. Parsley is biennial, so sow fresh seed in late summer for a crop the following year. If a pocket slumps or the compost sinks, top it up in spring — a pallet planter, looked after, will give you five or six seasons of herbs by the door.