Why a raised bed earns its keep

If your ground is heavy clay, stony, or not much more than builder's rubble under a skim of turf, a raised bed is the quickest route to a decent crop. You stop fighting the soil you have and start with something you have made yourself. There is a practical side too: raised beds warm up faster in spring, drain away the worst of a wet British winter, and save your back because you are not bending to ground level. Roots stay loose and easy to lift, weeds are simpler to pull, and a defined edge keeps the lawn where it belongs. For anyone with carrots on their wish list, it is close to essential — carrot fly and forked roots are both easier to manage in a bed you control.

Pick the site and get the size right

Vegetables want sun above all else: six hours a day as a minimum, eight is better. Avoid the north side of a fence or hedge, and stay clear of the drip line of large trees, which will steal both water and nutrients. Shelter from prevailing wind helps, but not so much shelter that air sits still and encourages mildew.

On size, the golden rule is never make a bed wider than you can comfortably reach across. For most people that means 1.2m wide, which lets you work from either side without treading on the soil. Length is up to you — 2.4m is a good, manageable standard. Allow 25–30cm of depth for salads, carrots and beans; go to 45cm if you have a bad back, are on a slope, or are building over concrete. Leave paths of 45–60cm between beds, and 90cm where a wheelbarrow needs to turn. Where you can, run beds north to south so plants do not shade one another.

Timber, brick or block: building the frame

Timber is the cheapest and simplest option. Pressure-treated timber lasts well over a decade, and 50mm x 150mm boards screwed into corner posts make a solid bed in an afternoon. Avoid old railway sleepers, which can leach creosote, and anything you cannot identify. There is no need to line the inside with plastic; the wood will weather and that is fine. Heat-treated pallet collars, stamped HT, are another cheap and perfectly sound choice.

Brick and block beds cost more and take longer, but they last for decades and look well in a small garden. Dry-lay them on a bed of sharp sand with a firm footing, or mortar them if you want them to stay put. Whichever material you choose, get the frame level — a bed that slopes will pool water at one end and dry out at the other.

Filling the bed: what actually goes in

The commonest mistake is filling a new bed entirely with bagged multipurpose compost. It shrinks alarmingly, runs out of nutrients within weeks and leaves you topping up for ever. Build it in layers instead.

On bare ground, start by laying down overlapping cardboard to smother the weeds beneath. Then aim for roughly half good topsoil, a third well-rotted manure or garden compost, and the rest peat-free multipurpose to lighten the mix. If your bed sits on a hard surface, put 10cm of gravel in the base for drainage before the cardboard. Fork it all together, water it well, and let it settle for a fortnight before planting. Fill to within 3cm of the rim so there is room for a mulch and for watering without it running off.

Aim for a slightly acid to neutral soil, around pH 6.5, which suits most vegetables. Do not add fresh manure to a bed destined for carrots or parsnips — it makes them fork.

What to sow in the first season

• Carrots. This is where a raised bed really pays off. Deep, stone-free, light soil gives you straight roots. Sow thinly from April to June in rows 15cm apart, and thin to 5cm as soon as the seedlings are handleable. A fine mesh barrier over the row is the most reliable defence against carrot fly.
• Salads. Lettuce, rocket, spinach, radish and spring onions all crop fast and suit a bed near the kitchen door. Sow little and often — a short row every fortnight from March to August — rather than one big sowing that bolts in July. Choose bolt-resistant varieties for midsummer and keep the soil consistently moist.
• Beans. Runner and climbing French beans are hungry, thirsty plants that reward a rich bed. Dig a trench a spade deep, half-fill it with kitchen compost and torn-up cardboard, backfill, and sow on top in late May once frost has passed. Give climbers a wigwam of canes at the northern end so they do not shade the rest of the bed; dwarf French beans are a fine choice for a windy site.

Use any gaps for quick crops: radishes between carrot rows, a few cut-and-come-again leaves along the edge of the beans.

Looking after it through the year

A raised bed dries out faster than open ground, so water properly rather than often. In dry spells, a good soak of around 20 litres per square metre once or twice a week beats a daily flick of the hose, because it drives roots down. Water in the morning, straight to the roots. A 5cm mulch of garden compost or straw after planting will halve the work.

Feed according to what you are growing: leafy crops want nitrogen, while beans and tomatoes want potash once they start flowering. A general-purpose organic fertiliser at the start of the season covers most needs.

Finally, keep the bed moving. Rotate your groups — legumes, brassicas, roots, potatoes — so the same family is not in the same spot two years running. Each autumn, top the bed up with 5cm of compost and tuck it up under a mulch. Do that and you will barely need to dig again.