Why Raised Beds Earn Their Keep

Anyone who has gardened on heavy clay, or on thin chalk over rock, will tell you the same thing: raised beds change the game. Soil in a bed sits above the surrounding ground, so winter rain drains through rather than pooling around your seedlings' roots. Come February, that same free-draining structure means the soil warms far more quickly than the cold, waterlogged ground either side of it. You can often sow a fortnight to three weeks earlier than you would in open ground, which matters enormously in a short British growing season.

There are other quiet benefits. You never walk on a raised bed, so the soil stays loose and crumbly without annual forking. You control what goes in it, which means you can grow acid-loving blueberries or free-draining carrots without fighting your natural soil type. And the working height saves your back — 15cm is a kindness, 30cm is a luxury. Slug pressure is slightly reduced too once beds are edged and paths are kept clean.

Siting, Sizing and Choosing Timber

Most vegetables want sun, so a south or south-west facing spot is ideal, away from the rain shadow of hedges, walls and mature trees. Trees are the sneaky ones: their roots will travel several metres for moisture and nutrients, so keep beds well clear.

Width is the crucial measurement. Make beds no wider than 1.2 metres, so you can reach the middle from either side without treading on the soil. Length is your choice — 2.4m to 3m suits most plots — and leave paths of 45–60cm between beds, or 90cm where a wheelbarrow needs to turn.

• Timber: tanalised softwood is cheap and lasts a decade or more; oak and larch are longer-lived and untreated. Avoid old railway sleepers unless you know they are free of creosote.
• Height: 15cm is fine for salads and most roots. Go to 25–30cm for deep beds, poor drainage, or if you want to garden from a stool.
• Thickness: 38mm boards hold their shape far better than flimsy 20mm gravel boards, especially once wet soil pushes outwards.

Building the Frame

Building a bed is a satisfying afternoon's work, not a project to dread.

• Clear the ground of perennial weeds, particularly couch grass and bindweed. Skim turf off and stack it upside down to rot into loam.
• Mark out with pegs and string, then check for square by measuring the diagonals — they should match. On a slope, cut in on the high side rather than trying to build level on air.
• Drive corner posts into the ground, then screw or bolt the boards to them. Use galvanised screws; they will not rust away in wet timber.
• Line the base with overlapping cardboard to smother weeds, then fill. There is no need for a membrane underneath, and you actively do not want one — worms and deep-rooting crops should be free to travel down.

The Filling Mix That Matters

What you put in the bed is what you will be eating for years, so do not skimp here. The reliable recipe is roughly equal parts by volume of topsoil, well-rotted compost and well-rotted manure. Topsoil gives body and holds moisture; compost brings humus, structure and slow-release nutrients; manure supplies the richness that hungry brassicas and courgettes adore.

Buying in that volume is expensive, so blend shamelessly. Garden compost, leafmould, spent mushroom compost and the contents of last year's grow bags all count. Never use fresh manure — it burns roots and harbours weed seeds — and be wary of manure from horses grazed on pasture treated with aminopyralid, which can damage tomatoes and beans for years.

For taller beds, save money by filling the bottom third with logs, brash, upturned turves and half-rotted material, then topping with your proper mix. It will settle as it decomposes, so fill to within 2–3cm of the rim and top up each spring.

Planting Up and Rotating Crops

Raised beds suit block planting rather than long rows, and the grid makes rotation almost automatic. Divide your beds into four groups: legumes, brassicas, roots and potatoes, and split each bed accordingly. Move the groups round each year to starve soil-borne pests and diseases of their hosts.

Spacing can be tighter than in open ground because the soil is deeper and richer. Salads go in at 15cm, dwarf French beans at 20cm, cabbages at 45cm. Water deeply but less often, aiming for the roots rather than the leaves, and mulch with compost or straw once the soil has warmed properly in late spring.

Net brassicas against pigeons and butterflies from the day they go in, and keep an eye on slugs during damp spells. A scattering of nematode treatment in early summer deals with the worst of them.

Looking After Beds Year on Year

A raised bed improves as it ages, but only if you feed it. Each spring, spread a 5cm layer of compost over the surface and let the worms pull it down, rather than digging it in. Sow green manure — field beans, phacelia, grazing rye — on empty beds over winter to protect bare soil and add organic matter.

Check the boards every couple of years, tightening screws and replacing any that have rotted at the base, and top up the levels after the soil settles. Treat a well-built, well-fed bed as a long-term investment: look after it properly and it will crop generously for fifteen years or more.