Building a Raised Bed from Reclaimed Timber

Why Reclaimed Timber Makes Sense

There's something quietly satisfying about building a raised bed from boards that have already lived a life. Maybe they came from a neighbour's fence that finally gave up, a pallet left behind on a building site, or a skip-bound wardrobe you dismantled on a Sunday afternoon. Reclaimed timber is cheap, often free, and it keeps good wood out of landfill. For a small plot, a raised bed solves several problems at once: you control the soil, you save your back, and you can grow carrots in a garden with three inches of compacted clay underneath.

The one thing that matters more than appearance is what the wood has been treated with. Old fencing, decking and timber yard offcuts are frequently soaked in preservatives you really don't want leaching into the soil that feeds your runner beans. If you can't identify the wood, use it for a compost bay or a path edge instead, and keep it away from edibles.

Choosing the Right Boards

Untreated timber is the gold standard, even though it won't last as long. Oak, sweet chestnut, larch and douglas fir are naturally durable and will give you eight to fifteen years in a raised bed. Scrap softwood will manage three to five years, which is still a decent return if it cost you nothing but a few hours with a claw hammer.

Here's what to look for when you're sorting through a pile:

• Avoid anything with a green or brown chemical stain, a creosote smell, or a waxy sheen. Railway sleepers are the classic trap — modern ones are usually tanalised, and old ones are soaked in tar.
• Check for rot or beetle holes. Sound the boards with a screwdriver. If it sinks in easily, the wood is already on its way out.
• Aim for 25–40mm thickness. Thinner boards bow under the weight of wet soil, especially over a two-metre run.
• Salvage the nails. Pull every last one, or you'll blunt your saw and curse loudly at the wrong moment.

If you're buying new timber instead, ask for untreated boards by name. Scaffold boards are popular but are almost always treated, so check before you commit.

Sizing It for a Small Space

A bed you can reach into from both sides should be no wider than 1.2 metres. If it sits against a wall or fence, keep it to 60–75cm so you can work it from one side. Length is more flexible, but 2.4 metres is a comfortable maximum that uses standard board lengths without much waste.

Depth is where people often overbuild. For salads, herbs, onions and most annual veg, 20–25cm of soil is plenty. For carrots, parsnips and maincrop potatoes, go to 30cm or more. If your bed sits on concrete or paving, you'll want at least 30cm to give roots room and to stop the soil drying out too fast in summer. On open ground, you can go shallower and let the roots find their own way down.

Building the Frame

Two boards high is the sweet spot for most plots — roughly 30cm once you allow for overlap. Cut your boards to length, then butt the corners together and fix them with galvanised timber screws, pre-drilled to stop the ends splitting. Corner posts made from 50mm square timber driven into the ground give the whole thing rigidity and stop the sides bowing outward.

Set the frame on levelled ground. Scrape the topsoil back, sit the bed down, and check it with a spirit level across both diagonals. A bed that's out of level will drain unevenly, and one corner will always look parched. Once it's true, screw through the posts into the boards and give the whole frame a gentle nudge to check for wobble.

Line the inside with a permeable membrane before you fill. This is the step most people skip. A woven landscape fabric or an old piece of breathable ground-cover cloth stops soil washing out through the gaps while letting surplus water drain away. Staple it to the inner face, leaving the top 5cm clear so you can still see the wood. Don't use plastic sheeting — you'll create a bathtub, and your plants will rot at the roots after the first wet fortnight.

Mixing the Perfect Fill

Good raised bed soil is roughly a third topsoil, a third compost, and a third something gritty to open it up. That's the honest, workable ratio. For a bed measuring 2.4m by 1.2m by 30cm deep, you're looking at around 850 litres — a serious amount, so start collecting.

• Topsoil: buy in bulk bags or borrow from a spoil heap, but avoid anything heavy and grey with no worms in it.
• Compost: your own is best, but shop-bought multi-purpose or well-rotted manure works fine. If you use manure, make sure it's from a supplier who doesn't use aminopyralid weedkiller — it wrecks tomatoes and potatoes for years.
• Grit or sharp sand: horticultural grit at roughly one part in ten improves drainage and stops the mix caking.

Mix it in a barrow or on a tarpaulin, then tip it in and firm gently as you go. Don't stomp it down — you want a crumbly, open structure, not concrete. Fill to within 3–5cm of the rim so there's room for a mulch later.

Planting Up and Keeping It Going

Let the bed settle for a week or two before sowing, watering it well so the levels even out. Then plant with confidence: salads, radishes and beetroot in spring, beans and courgettes through summer, and garlic or overwintering broad beans if you want something in the ground year-round.

Top up with a 5cm mulch of compost each autumn. It feeds the soil, suppresses weeds, and slows evaporation. Check the boards every couple of years — if a section has softened, replace it while the bed is empty in winter. Treated this way, a reclaimed-timber bed will keep producing for a decade or more, and it'll look far better than anything flat-packed.