How to Build a Simple Raised Bed for Vegetables

Why a raised bed is worth the effort

Raised beds warm up faster in spring, drain better in wet winters, and stop you treading on the soil. For a small UK garden, a simple timber frame is one of the best investments you can make. You control the soil, so you can grow salads, carrots and herbs even if your ground is heavy clay or stony. The bed also lifts the growing area closer to you, making sowing, weeding and harvesting kinder on the back.

You do not need a grand design. A single bed about 1.2 metres wide and 2.4 metres long is easy to reach across. Keep it at least 20 centimetres deep; 25 to 30 centimetres is even better for roots and moisture retention.

Choose untreated timber and build the frame

Use untreated timber for the frame. Treated wood may contain preservatives you would rather keep away from edible crops, and old railway sleepers can carry creosote. Good choices include untreated pine, larch or oak boards. A thickness of 2.5 to 5 centimetres is sturdy enough. For a bed 20 centimetres deep, you need boards at least 20 centimetres wide.

Cut four sides: two at 2.4 metres and two at 1.2 metres. You will also need four corner posts, roughly 5 x 5 centimetres and 40 centimetres long. Clear perennial weeds such as bindweed and couch grass. Mark out the rectangle with string and canes, checking the diagonals are equal.

Lay the boards on a flat surface. Position a corner post at each corner, flush with the top edge. Drill pilot holes to stop the timber splitting, then screw through the boards into the posts. Use two screws per board per corner. Stand the frame up and check it is level. Tap the posts into the ground with a lump hammer until the frame feels solid. If deep-rooted weeds are a problem, line the base with a single layer of cardboard; it will rot down and suppress weeds for the first season.

Fill with topsoil and compost

Aim for roughly 60 per cent topsoil and 40 per cent compost by volume. A bed 2.4 metres by 1.2 metres and 20 centimetres deep needs about 600 litres of material: roughly 360 litres of topsoil and 240 litres of compost. Topsoil gives body and holds moisture; compost adds nutrients, structure and life.

Use a mix of garden compost, well-rotted manure and leafmould if you have them. Bagged peat-free compost is fine, but blend it with topsoil so it does not dry out and shrink. Avoid subsoil from a building project. If your topsoil is heavy clay, add extra compost and a few handfuls of horticultural grit. If it is sandy, add more compost to improve water retention.

Fill in layers, firming gently as you go. Do not compact it by stamping. Leave the surface 2 to 3 centimetres below the top of the frame so you can water without spilling. Water well and let it settle for a few days before sowing.

Sow salad crops for a fast reward

Salad crops are perfect for a new raised bed. They grow quickly and can be sown in succession from early spring to late summer. Start with lettuce, rocket, radish, spring onions, spinach and cut-and-come-again mixes. For a continuous supply, sow a small pinch every two to three weeks rather than all at once.

Rake the surface to a fine tilth. Sow seed thinly in shallow drills, about 1 centimetre deep for lettuce and radish, and 2 centimetres for spinach. Space rows 15 to 20 centimetres apart. Cover with soil, water gently with a fine rose, and keep the surface moist until germination. Thin seedlings as they grow: lettuce to 20 centimetres, radish to 5 centimetres, spring onions to 5 centimetres. The thinnings are excellent in salads.

• Water little and often; dry spells make salad leaves bitter and bolt.
• Shade late sowings in hot weather, or grow heat-tolerant varieties.
• Protect young seedlings from slugs and pigeons with a cloche or fleece.
• Harvest outer leaves of lettuce and spinach to keep plants cropping longer.

Keep the bed productive all year

After your first salad harvest, top up the bed with a 2 to 3 centimetre layer of compost. This feeds the soil and replaces what the crops have used. Rotate what you grow: follow salad leaves with carrots, beetroot or dwarf French beans. In autumn, sow winter salad, lamb’s lettuce or winter purslane under a cloche. A raised bed stays workable in wet weather, so you can keep growing when the rest of the garden is sodden.

Check the timber each year. Untreated boards will weather and may need replacing after five to ten years, depending on the wood and the dampness of your site. That is a small price for fresh, tender vegetables within weeks. Start small, build it well, and let the soil do the rest.