A raised bed earns its space

If your garden is little more than a courtyard, a balcony with a view of the wheelie bins, or a narrow strip behind the kitchen, a raised bed can turn a patch of paving into something genuinely productive. It raises the growing layer above tired ground, lets you control the soil completely, warms up faster in spring, and saves your back from bending double. For anyone growing vegetables in a small space, it is often the single best investment of a weekend.

The version described here is deliberately simple: four boards, a lined base and a decent growing medium. No joinery skills required, no specialist tools beyond a saw and a drill.

Choosing rot-resistant timber

Timber in contact with damp soil will rot eventually, so pick a species or treatment that buys you a decade rather than a season. Pressure-treated softwood — often sold as tanalised — is the sensible budget choice and is perfectly safe for edible crops under current UK regulations. It will typically give you ten to fifteen years. If you would rather avoid chemical treatment, larch, oak, sweet chestnut and cedar all weather well, though they cost more and oak in particular is heavy work to move.

Aim for boards around 200mm to 300mm wide and at least 25mm thick; thicker boards resist bowing when the soil pushes outwards. A bed 2.4m long by 1.2m wide is a classic because you can reach the middle from either side without stepping on the soil. In a tight space, 1.2m by 1.2m works beautifully, and 900mm by 1.8m fits neatly along a wall.

• Corner posts: 50mm x 50mm posts, 400mm long, set just inside each corner to screw the boards into.
• Fixings: galvanised or stainless screws, 60mm to 75mm — ordinary steel will rust away.
• Height: two boards deep on their edge, roughly 400mm, suits most vegetables and saves a lot of stooping.
• Avoid: old railway sleepers of uncertain origin, creosote-treated timber and any salvaged wood you cannot identify.

If you are placing the bed on hardstanding, you can also buy slotted timber kits or stack reclaimed bricks, but plain boards remain the cheapest and most forgiving option.

Preparing the base and lining it

Decide first whether your bed sits on soil or on paving. On soil, you have the option of leaving the base open so roots and worms can travel freely — the best choice if the ground beneath is not compacted builder's rubble. Fork it over lightly before the frame goes down.

On paving, you need a barrier that stops weeds but still lets water drain away. Line the base with a single layer of thick cardboard, overlapped generously, then sit the frame on top. Cardboard smothers annual weeds and slowly breaks down. Avoid solid plastic sheeting or a sealed membrane: water will pool, roots will sour, and you will spend the summer wondering why everything is yellow.

If the bed sits over a hard surface, add a thin layer of gravel or broken crocks at the very bottom to help drainage, and consider standing the frame on a couple of battens so air can move underneath. Before filling, check the frame is level — a five-minute job with a spirit level that prevents a permanently lopsided bed.

Filling with a soil and compost mix

Do not simply tip in bags of multipurpose compost. It dries out, shrinks and slumps, and it holds nutrients poorly over a full season. A better fill is roughly 60 per cent topsoil to 40 per cent organic matter, which gives you body, water retention and fertility in one go.

• Topsoil: buy loam-based topsoil in bulk bags, or use soil from elsewhere in the garden if it is decent.
• Compost: your own garden compost is ideal; otherwise peat-free multipurpose works fine as part of the mix.
• Well-rotted manure: a couple of barrowloads per bed, no more, or you will get leafy growth and few roots.
• Grit or sharp sand: a handful or two if your mix feels heavy and sticky.

Fill to about 25mm below the rim so there is room to water without it running straight off. Then let it settle for a week or two before planting, topping up as it sinks. From then on, a mulch of garden compost each spring is all most beds need.

Siting it for sun and shelter

Most vegetables want at least six hours of direct sun a day, so a south-facing or south-west-facing spot is the prize. Watch your garden through a spring day before committing: that corner which looks sunny at nine in the morning may be in shade by two.

Keep the bed away from the drip line of trees and hedges, whose roots will quietly invade and steal both water and nutrients. Leave a path of at least 600mm on the long sides so you can kneel, wheel a barrow and reach in comfortably. If the site is windy, a low hedge or a trellis of climbing beans will do more for your courgettes than any amount of feeding.

Finally, put it near a water butt or an outdoor tap. A raised bed dries out faster than open ground, and the bed you can reach with a hosepipe is the bed that actually gets watered in July. Get those four things right — sound timber, a drained base, a proper mix, and a sunny, accessible spot — and the rest is just sowing, watering and, with any luck, far too many courgettes.