Why raised beds earn their keep by the sea

Coastal soil is rarely generous. It may be thin, stony and quick to drain, or heavy clay that sits wet and cold all winter and then bakes to brick in July. Add salt-laden wind and a shorter growing season, and open-ground vegetable growing can feel like an uphill struggle. Raised beds do not solve every seaside problem, but they tip the odds firmly in your favour. Filled with a decent blend, the soil in a raised bed warms two to three weeks earlier in spring, drains freely after a downpour, and sits above the worst of the salt splash that coats low ground during gales. They also give you a defined area to improve year after year, rather than trying to tame an entire plot at once. On exposed sites, the extra height and a little shelter can make the difference between a crop of dwarf beans and nothing at all.

Siting and sizing the beds

Choose the sunniest spot you have, ideally somewhere that catches at least six hours of direct light in midsummer. Run the long axis of the beds across the prevailing wind rather than parallel to it, so the beds themselves act as low baffles and the wind skims over rather than scouring along the rows. A living windbreak – a hedge of escallonia, sea buckthorn or griselinia – planted three or four metres away will slow the wind without casting too much shade. Keep the beds themselves practical: no wider than 1.2m, so you can reach the middle from either side without treading on the soil. Paths of 45cm suit a wheelbarrow; go to 75cm if you use a wheelchair or want room for a kneeling stool.

Depth matters more than most people expect. A bed 20–25cm deep is ample for salads, herbs, radishes and beetroot. Allow 30cm for carrots and onions, and 45cm if you want to grow maincrop potatoes, parsnips or brassicas that need a firm, deep root run. On very stony ground, sit the frame directly on the surface, line the base with a double layer of plain cardboard and let the worms do the rest.

Choosing untreated timber

Untreated timber is the right choice for a vegetable plot, and it lasts longer than sceptics suggest. Oak and sweet chestnut are the traditionalists' favourites and can give fifteen years or more. Larch and Douglas fir are cheaper, softer and more likely to last eight to twelve years before the boards start to crumble at the base. Boards of 150 x 50mm with corner posts of 75 x 75mm driven 30cm into the ground will shrug off most winter gales, especially if you add a mid-point post on beds longer than 2.4m.

• Avoid creosote-treated railway sleepers, which can leach into the soil.
• Skip old pallets and reclaimed timber unless you know what was stored or treated on them.
• Do not line the inside with plastic sheeting – it traps water against the wood and shortens its life.
• Fix boards with galvanised or stainless screws, as coastal air eats ordinary steel quickly.

Filling: the soil-compost blend

Filling a bed is the expensive part, so get the mix right first time. Aim for roughly 40 per cent topsoil, 40 per cent well-rotted compost or manure, and 20 per cent coarse grit or sharp sand if your native ground is heavy. On sandy coastal ground, swap the grit for extra compost and a little loam to help it hold water and nutrients. Pure compost looks lovely but shrinks dramatically in the first season and dries out fast in wind, so it is worth the effort to blend.

• Roughly one barrowload of blended mix fills one square metre to 20cm deep.
• Seaweed, well rinsed and dug in or composted first, is a superb local amendment.
• Leave a 5cm gap below the rim so mulch and water stay put.
• Water thoroughly to settle the mix, then top up before sowing.

Planting for wind, salt and a short season

Once the beds are in, choose crops that suit the site rather than fighting it. Dwarf French beans, chard, kale, beetroot, carrots, radish, spring onions and cut-and-come-again salad leaves all cope well with coastal conditions. Purple sprouting broccoli and winter cabbage are reliably sturdy. Tomatoes, peppers and courgettes are possible in a warm, sheltered corner, but expect to give them a cloche or fleece in early summer. Plant in blocks rather than long thin rows so the plants shelter one another, and earth up or stake anything tall before the first autumn gales arrive.

• Use fleece or fine netting over hoops to blunt wind and deter carrot fly and cabbage white butterflies.
• Peg netting down firmly with ground staples – coastal gusts will lift anything loose.
• Sow small quantities every three weeks for a steady supply rather than one glut.

Watering, mulching and keeping beds productive

Wind dries soil far faster than sun does, so mulch every bed with 5cm of compost, straw or grass clippings once the ground has warmed. Collect rainwater in butts – coastal tap water is often hard and hosepipe restrictions arrive in dry summers just when you need water most. In autumn, clear spent crops, spread a fresh layer of compost and sow a green manure such as field beans or grazing rye on empty beds to hold nutrients through the winter rain. Top up the levels each spring, check the boards for rot, and replace the odd plank as needed. Looked after this way, a set of raised beds will keep feeding you from a windswept plot for many seasons.