James Whitaker
Why scaffold boards make excellent raised beds
Scaffold boards have become the go-to timber for allotment holders and kitchen gardeners, and for good reason. A standard board measures roughly 225mm wide and 38mm thick, which is far sturdier than the flimsy gravel boards sold in garden centres. That thickness means a raised bed built from them will hold back a serious depth of soil without bowing outwards, even after a wet winter. They are usually available second-hand from reclaim yards or direct from scaffolding firms, often for a fraction of the price of new timber, and they weather to a handsome silvery grey if you leave them bare.
There is also a practical bonus: because scaffold boards are a consistent size, you can plan a bed on paper and know exactly how it will go together. No wrestling with warped, mismatched planks.
Planning the size and gathering your materials
The most useful size for a kitchen garden is a bed measuring around 2.4m long by 1.2m wide, with boards stacked two high to give a soil depth of roughly 450mm. That width means you can reach the middle from either side without treading on the soil, and the depth suits everything from lettuce to maincrop potatoes.
Here is the neat part: four standard 3.9m scaffold boards will give you exactly what you need. Cut each board into one 2.4m length and one 1.2m length, leaving a short offcut for bracing. That yields four long sides and four short sides, which is precisely enough to build the bed two boards high. Before you start, gather:
- Four 3.9m scaffold boards (or eight pre-cut lengths)
- Four corner posts, roughly 75mm x 75mm and 600mm long
- 100mm galvanised timber screws, about 40 of them
- A saw, cordless drill, spirit level, tape measure and set square
- A mallet and some string line for setting out
Position the bed on level ground, ideally on a sunny site that has not grown potatoes or tomatoes in the last couple of years. Mark out the footprint with string and check the diagonals are equal, which guarantees square corners.
Building the frame
Drive the four corner posts into the ground at each corner, leaving about 450mm above the surface. Check each one with the spirit level as you go — a leaning post will throw the whole bed out and make the boards twist. Once the posts are firm, screw the first layer of boards to them, starting with the long sides. Use two screws per board end, driven through the board into the post, and pre-drill near the ends to avoid splitting the timber.
When the first layer is complete, screw the second layer on top. Stagger the joints so the corners of the upper boards overlap the joints of the lower ones, rather than sitting directly above them. This simple trick adds a great deal of rigidity and prevents the corners from splaying. Finish by checking the whole structure for level and giving any high posts a tap with the mallet. If you have offcuts left, screw a short brace across the inside of each long side at the midpoint for extra insurance.
Treating the timber
Scaffold boards are usually untreated or very lightly treated, so a little protection will add years to their life. Brush on a plant-safe wood preservative or a couple of coats of raw linseed oil, paying particular attention to the end grain and any cut edges, which soak up water fastest. Do this before you fill the bed, ideally on a dry day, and allow at least 48 hours to dry.
What you should avoid is creosote or any solvent-based treatment that could leach into your soil. Modern pressure-treated timber is generally considered safe for growing, but as a rule, if a product carries a warning about plants or livestock, keep it away from your beds. Lining the inside with a breathable membrane is optional; it slows rot, but can trap moisture against the boards, so many growers simply let the timber breathe.
Filling the bed
A bed of this size holds roughly 1.3 cubic metres of material, which is a lot to buy in bags. Bulk delivery of topsoil and compost is far more economical. Aim for a mix of about 60 per cent topsoil, 30 per cent compost or well-rotted manure, and 10 per cent sharp sand for drainage on heavy clay.
You can save a surprising amount of soil by filling the bottom third with scavenged material — logs, pruned branches, cardboard, and half-rotted garden waste. This improves drainage, feeds the soil life below, and slowly breaks down over the coming seasons. Just make sure the top 300mm is good-quality growing medium, as that is where your roots and seeds will be working. Firm the fill gently as you go, then water it thoroughly and leave it to settle for a week or two before planting.
Getting the most from your first season
Once your bed is filled, resist the urge to dig it over. A no-dig approach — spreading a layer of compost on top each spring and letting the worms do the work — suits raised beds perfectly and keeps the soil structure intact. Sow or plant into the top layer, spacing crops according to the packet, and keep the surface mulched with compost or straw to hold moisture through dry spells.
Top up the bed each autumn with a fresh layer of well-rotted manure or homemade compost to replace what your crops have taken out. Treated well, a scaffold board bed will give you a decade or more of productive growing, and the only maintenance it will ask of you is the occasional check that the screws are still tight.
