Building a Raised Bed from Reclaimed Timber

Why Reclaimed Timber Makes Sense

There is something deeply satisfying about turning a stack of old scaffold boards or weathered decking into a productive raised bed. Reclaimed timber costs little or nothing, keeps useful material out of landfill, and often has a character that new, tanalised wood cannot match. For UK gardeners, it is a practical choice — but only if you choose the right pieces. Avoid any timber that has been treated with creosote or old-style CCA preservatives, which can leach into your soil. Railway sleepers are best left alone unless you know their history. Look instead for untreated oak, sweet chestnut, larch, or old scaffolding boards that have been stored dry.

Before you commit, check every length for rot. Press a screwdriver into the wood — if it sinks in easily, or if you see soft, crumbly patches, white fungal threads, or woodworm holes, reject it. A little surface weathering is fine; structural decay is not. Also remove any nails, screws, or staples, as these will blunt your tools and can injure you later.

Sourcing and Preparing Your Timber

Good places to find reclaimed timber include salvage yards, local building sites (always ask first), online marketplaces, and skips — but never take without permission. Scaffolding boards are ideal: they are usually 3.9 metres long, 22.5cm wide, and about 3.8cm thick. You can cut them down to size with a handsaw or circular saw. For a raised bed, aim for a width of no more than 1.2 metres so you can reach the middle without stepping on the soil. A length of 2.4 metres is a classic size, giving you a bed that is easy to net and rotate.

Once you have your timber, give it a quick sand along the cut ends and any rough edges. If the wood is untreated and you want to extend its life, brush on a plant-safe preservative such as raw linseed oil or a beeswax mix. Do not use engine oil or old creosote. Let it dry for a few days before building.

Building the Frame

Start by marking out the bed on the ground. Remove any perennial weeds and roughly level the soil. For a sturdy frame, you need four corner posts — 75mm x 75mm timber is ideal — cut to the height of your boards plus 10cm to knock into the ground. If you are building on hard standing, use metal corner brackets instead.

Attach the boards to the posts using galvanised screws, 75mm long. Pre-drill to avoid splitting. Work around the bed, checking with a spirit level as you go. For beds longer than 2 metres, add a central brace across the middle to stop the sides bowing out when the soil is added. A try square will help you keep the corners true. Once the frame is complete, give it a gentle push — it should feel solid and immovable.

Lining the Sides

Lining the inside of your reclaimed bed is a simple step that pays off. It protects the timber from constant contact with damp soil and slows the rotting process, especially with older wood. Use heavy-duty polythene — 500 gauge or thicker — or damp-proof course membrane. Staple it to the inside of the boards, overlapping the corners neatly. Leave the bottom completely open so excess water can drain away and worms can move freely.

If your timber is untreated oak or sweet chestnut, which are naturally rot-resistant, you can skip the liner. But for most reclaimed wood, lining is a wise precaution. Avoid using old carpet or cardboard as a liner — they break down quickly and can harbour pests.

Filling the Bed

The secret to a productive raised bed is the growing medium, not the timber. A mix of roughly 60% topsoil and 40% well-rotted compost or manure works well for most vegetables and flowers. Buy screened topsoil if you need to bring it in, and check it is free from weeds and stones. If your existing soil is heavy clay, add a bucket of horticultural grit per square metre to improve drainage.

Fill the bed in layers, firming gently with your hands as you go. Do not compact it heavily — you want a loose, crumbly texture. Leave the surface about 5cm below the top of the boards to allow for watering and mulching. Water thoroughly and let the bed settle for a week before planting. For most crops, a soil depth of 25–30cm is plenty; for carrots and parsnips, aim for 40cm.

Making It Last and What to Grow

Reclaimed timber will not last forever, but you can get many years from it with a little care. Check the boards each spring. If a section has rotted, replace it with a fresh piece rather than rebuilding the whole bed. Top up the soil with compost each year, and keep the liner intact. A layer of mulch — straw, grass clippings, or leaf mould — will suppress weeds and conserve moisture.

As for planting, raised beds are perfect for salads, radishes, dwarf beans, and herbs. The improved drainage suits garlic and onions, whilst the warmer soil in spring lets you start early. Rotate your crops each year to avoid pests and diseases. And remember: the best raised bed is the one you actually fill, so do not wait for perfect timber. A slightly wonky, reclaimed frame full of healthy vegetables is a beautiful thing.