How to Build a Simple Raised Bed for Vegetables

Why a raised bed earns its keep

A raised bed is the quickest way to turn a tired patch of lawn, a concrete slab or the corner of an allotment into ground that genuinely grows something. The soil warms faster in spring, it drains far better through our wet winters, and you never again compact the earth by walking on it. On a small plot — a back garden, a half-plot, a strip beside the shed — one well-built bed will crop harder than a much larger piece of open ground.

Build it once, fill it properly, and you have a growing space that will last a decade or more.

Picking the right spot and size

Sun comes first. Most vegetables want six hours of direct light a day, so watch your plot at midday and early afternoon before committing. Keep the bed within reach of a water butt or an outdoor tap, because a raised bed dries out faster than open ground and you will be watering it more often, not less.

Now the size. A width of 1.2 metres is the golden rule — you can reach the middle from either side without treading on the soil, which is the whole point. A length of 2.4 metres is a good standard, giving you just under three square metres of growing space. If you are building several, run them the same length so they look tidy and you can use the same cutting list.

Leave paths of 45 to 60 centimetres between beds. That sounds generous when you are drawing it out, but you need room for a wheelbarrow and for kneeling down without bruising your ribs on the timber.

Try to site the bed on level ground. If the only spot you have slopes, either terrace it into two shorter beds or dig the frame into the higher side so no daylight shows underneath.

Buying the timber

Treated softwood is perfectly adequate and much cheaper than oak or plastic. The standard size is 150mm x 50mm — sometimes sold as 6x2 — in 2.4 metre lengths. For a bed measuring 2.4m x 1.2m you need two full lengths, plus a third cut into two 1.2 metre ends.

You will also want four corner posts, roughly 75mm x 75mm x 300mm, to screw the sides into. This is far stronger than butting boards together and means the frame will not splay out once it is full of wet soil. Use 100mm exterior-grade screws.

Two warnings. Avoid old railway sleepers, which were often soaked in creosote and are not suitable for food crops. And avoid mystery reclaimed timber — you cannot tell what it was treated with.

For a bed this size, expect to spend somewhere between £40 and £70 on timber and fixings, depending on what your local yard stocks.

Building the frame

Choose a dry afternoon; this is a two-hour job at most.

• Clear the ground of perennial weeds, but do not dig it over. You are building on top of what is there.
• Lay the four boards out on a flat surface and mark where the corner posts will sit.
• Screw the long sides to the posts first, then attach the short ends, checking for square by measuring the diagonals — they should match.
• Lift the frame into position and check it is level with a spirit level on all four sides. Adjust by sliding soil under the low corners.
• Press the frame down so the bottom edge sits 20 to 30mm into the soil, closing any gaps against slugs and wind.
• Line the inside with a permeable membrane if you want to slow the rotting of the boards, but leave the base open to the soil below.

For most vegetables a single board height of about 15 centimetres is fine. Carrots, parsnips and maincrop potatoes prefer 30 centimetres, so stack two courses if those are on your list.

Filling it properly

Work out the volume before you order anything. A 2.4m x 1.2m bed filled to 30 centimetres needs roughly 0.85 cubic metres of material — about one bulk bag.

A good general mix is roughly 60 per cent topsoil, 30 per cent peat-free multi-purpose compost and 10 per cent well-rotted manure. On heavy clay, add a couple of buckets of horticultural grit. On light sandy soil, lean more heavily on the compost.

If you would rather not buy topsoil, use the no-dig method: cover the ground with a thick layer of cardboard, overlapping the edges, soak it well, then fill the bed entirely with compost and well-rotted manure. It costs more per bag but you will be sowing into it within weeks.

Fill to within 25mm of the top, firm it lightly with your hands — not your boots — and water it thoroughly. Leave it to settle for a fortnight before sowing.

Planting up and keeping it productive

Once settled, the bed is ready. Direct-sow salads, radish, beetroot, carrots and spring onions in short rows across the width, and raise brassicas, courgettes and beans in modules for planting out later. A 1.2 metre width suits block planting better than long rows, which makes better use of the space and shades out weeds.

Water deeply rather than little and often, aiming for the roots. Mulch the surface with 50mm of compost each spring, and top the bed up as the contents settle — it will drop by a few centimetres every year.

Rotate your crops between beds each season, keep the paths clear, and a single raised bed will quietly outproduce a vegetable patch three times its size.