How to Build a Simple Raised Bed for Vegetables

Why a Raised Bed Earns Its Place

Anyone who has gardened on heavy clay, or on a patch of ground that floods every February, soon learns the value of growing above the soil rather than in it. A raised bed gives you drainage you can rely on, a depth of good loam you have mixed yourself, and a working height that saves your back. The soil warms earlier in spring, so you can sow a fortnight ahead of the open ground, and you never again tread on the beds you are trying to cultivate.

They are also, mercifully, simple things. A raised bed is a box without a bottom. What matters is that it is square, level and made from timber thick enough to hold its shape for a decade or more. Most of the beds I have built have cost very little, because the timber was already lying about somewhere waiting to be useful.

Sourcing Reclaimed Timber Without Cutting Corners

Scaffold boards are the classic choice: roughly 220mm wide and 38mm thick, they make a generous single-height bed and last well if raised off the ground. Decking boards, old pallet timber and salvaged floorboards all work too, though thinner boards want doubling up or supporting more often.

What you must avoid is anything that has been treated with creosote, old engine oil or other unknown brews. Old railway sleepers are best left alone. Look for timber that is either untreated, heat-treated, or properly pressure-treated for garden use. If you are unsure of its history and it will hold soil against your carrots, line the inside with a sheet of heavy-duty polythene or butyl, punctured at the base for drainage.

• Boards: 38–50mm thick, 150–225mm wide. Two courses stacked gives a bed around 300mm deep.
• Corner posts: 75 x 75mm or 100 x 100mm, cut roughly 100mm longer than the finished height so they can be driven into the ground.
• Fixings: galvanised or stainless steel screws, 75–100mm long. Ordinary steel screws will rust through in a couple of wet seasons.
• Tools: a panel saw, cordless drill, spade, club hammer, tape measure, spirit level and a ball of string.

Setting the Size and Marking Out

Keep the bed no wider than 1.2m, so that you can reach the middle comfortably from either side without climbing in. Length is your own affair — 2.4m suits a standard scaffold board with very little waste, and gives a satisfyingly generous growing area.

Choose a spot in full sun, within reach of a water butt or tap, and away from the drip line of any large tree. Slash down the perennial weeds such as couch grass and bindweed, then lay a thick layer of cardboard over the footprint and soak it. This smothers what is underneath without a single drop of weedkiller.

Mark out the rectangle with pegs and string, checking that the corners are square by measuring both diagonals — they should be identical. Then check the levels. A bed that is 25mm out across its length will look wrong forever and will sit unevenly in the ground.

Cutting and Assembling the Frame

Cut your boards to length in pairs, so the two long sides match exactly and the two short sides do too. Lay them out on flat ground and dry-fit the rectangle before you drive a single screw.

Set a corner post in each corner, standing proud at the top, and screw the boards to it from the outside. Drill pilot holes first — reclaimed timber splits easily, especially old, dry boards. Use two screws per board end, staggered slightly so the grain is not weakened along one line.

If you are building two courses high, run the second course with its joints offset from the first, as you would lay bricks. This ties the whole structure together and stops it racking. For extra rigidity, fix a small metal angle bracket inside each corner, or screw a short offcut of timber across the inside joint.

Once the frame is built, lift it into position on the cardboard, check the levels again, and drive the corner posts into the ground with the club hammer. Backfill around the outside with soil and firm it.

Filling the Bed and Planting It Up

Do not simply shovel in the subsoil you dug out when levelling. A raised bed is a chance to give your plants something better. Fill in rough layers: a base of garden soil, then well-rotted manure or compost, then a top 100mm of bought or homemade compost mixed with a little sharp sand or grit if your soil is heavy.

Roughly two parts topsoil to one part compost is a sound starting point. Tread it lightly as you go, water it well, and let it settle for a week or two before sowing — it will drop by 25mm or so, and you can top it up.

Small Habits That Make Beds Last

• Never stand or kneel on the soil; work from the paths.
• Mulch each autumn with compost or leafmould to keep the level up and the worms busy.
• Check the screws each spring and tighten or replace any that have worked loose.
• Treat the outside faces of untreated timber with a water-based, plant-safe preservative, never the inside.
• Rotate your crops between beds, and top up the soil level every couple of years.

Built well, a reclaimed-timber bed will give you eight to fifteen years of good service. It is one of the few jobs in the garden that repays a single afternoon's work for the best part of a decade.