How to Build a Simple Raised Bed from Reclaimed Timber

Why Raised Beds Earn Their Keep on a Small Plot

Anyone working a couple of acres, a half-acre paddock, or a long thin strip behind the cottage soon learns that raised beds are less of a fashion and more of a piece of practical kit. They warm up earlier in spring, they drain better in a wet summer, and they let you grow carrots in ground that would otherwise be heavy clay. Best of all, they turn awkward spaces into productive ones: the sunless corner by the shed, the slope behind the greenhouse, the strip of gravel where nothing was ever going to grow.

Building them from reclaimed timber keeps the cost down and stops good boards going to landfill. A single run of scaffolding boards can yield three or four beds, and the whole job is a pleasant afternoon's work with a saw, a drill and a decent spirit level.

Choosing Reclaimed Timber That's Safe for Growing

Not all salvaged wood is suitable. You are looking for untreated boards — clean, sound timber with no rot, no flaking paint and no chemical staining.

• Scaffolding boards are the gold standard: roughly 225mm wide, 38mm thick and usually about 2.4m long. Strong, reasonably straight and long-lasting above ground.
• Old floorboards and joists work well if you can get them in decent lengths. Thicker joists are ideal for cutting into corner posts.
• Pallet wood is fine for shorter beds, but avoid any pallet stamped MB, and steer clear of anything that has carried chemicals, paint or unknown liquids.
• Avoid creosoted timber, old railway sleepers and anything with a heavy tarry smell. These can leach into the soil and simply are not worth the risk around edibles.

Scrub salvaged boards with a stiff brush and let them dry before you build. If you want to extend their life, line the inside faces with a sheet of damp-proof membrane or a layer of heavy cardboard; both keep damp soil off the wood while still letting the bed breathe.

Sizing the Bed to Your Plot and Your Reach

The classic dimensions are 2.4m long by 1.2m wide, because you can reach the middle from either side without treading on the soil. On tighter plots, drop to 2.4m by 0.9m, or build square metre beds for herbs and cut-and-come-again salads. If a bed sits against a wall or fence, keep it under 60cm wide so you can still reach the back without clambering.

Depth matters more than width. Around 20–25cm of soil is plenty for salads, herbs, onions, chard and most brassicas. Go to 30cm or more for carrots, parsnips and maincrop potatoes, which need room to root down.

Measure your space honestly, including the paths between beds. A 60cm path is comfortable with a wheelbarrow; 45cm is workable if you are only carrying a trug.

Getting the Base Level Before You Fix Anything

A bed sitting proud on one corner will twist, open at the joints and eventually fail. Spend your time here and the rest is straightforward.

• Mark out the footprint with pegs and string, then strip the top layer of turf or perennial weeds.
• Check the ground with a long spirit level. On a gentle slope, dig the higher end in rather than trying to build a stepped bed.
• Firm the base with the back of a spade, and add 5–10cm of gravel or rubble if the site holds water.
• Lay a sheet of cardboard over the base to suppress weeds and feed the worms as it rots.
• On hard standing, use a membrane underneath and consider a shallow gravel layer so roots are never sitting in a puddle.

Corner Braces and a Frame That Stays Square

Butt-jointing boards with a couple of screws will hold for a season; proper braces will hold for a decade. Cut four corner posts from 75mm or 100mm square timber, each the full height of the bed. Set them inside the corners and fix the boards to them with 100mm galvanised screws — two per board end, with pilot holes drilled first to stop the timber splitting.

Work on a flat surface so the frame stays true. Once the first course is assembled, measure both diagonals: if they match, the bed is square. For a two-board-high bed, add a mid-rail on the long sides, or bolt a metal angle bracket across each internal corner. Reclaimed angle iron from a farm sale is perfect for this. Keep the top edge flush and smooth — you will be leaning on it for years, and splinters are a poor reward for good work.

Filling the Bed and the First Season

Aim for roughly 40 per cent topsoil, 40 per cent homemade compost or well-rotted manure, and 20 per cent leaf mould or spent mushroom compost. Pure compost sinks alarmingly and dries out in summer; a loamy mix holds together far better. Fill to within 3cm of the rim, firm gently with your hands rather than booting it down, and water well before planting.

You can sow or plant straight away. Top the bed up each autumn with a generous mulch of compost, and rotate your crops between beds year on year. Keep the paths mown, mulched with bark or laid with gravel, and the whole plot will look cared for even in the depths of February. A well-built reclaimed bed should give you fifteen years of harvests — which, on a smallholding, is about as good a return as you will ever get from a pile of old boards.