Why Raised Beds Suit Small British Gardens

If your patch is a postage stamp, or the soil is heavy clay that bakes solid in July and floods in February, a raised bed is the best weekend's work you can put into a garden. You get complete control over the growing medium, proper drainage after a wet British winter, and soil that warms up weeks earlier in spring — which means earlier salads and a longer season.

The one measurement that matters most is width. Keep the bed 1.2m across and you can reach the middle from either side without ever standing on the soil and compacting it. Length is flexible: 2.4m fits neatly into most gardens and divides into tidy square-metre planting blocks for crop rotation.

Choosing Timber and Working Out Your Sizes

For beginners, 38mm x 150mm pressure-treated timber is the sweet spot. It is affordable, easy to handle and rot-resistant for a decade or more. Avoid anything dipped in creosote, and steer clear of old reclaimed sleepers of unknown origin — whatever is in that timber will end up in your carrots.

A single board height of 150mm is plenty for salads, herbs, onions and most shallow-rooted crops. Go to two boards high, around 300mm, if you want carrots, parsnips and maincrop potatoes, or if you are building on a patio where there is no soil beneath.

For a 1.2m x 2.4m bed standing 300mm high, you will need:

• Four lengths of 2.4m timber for the long sides
• Four lengths of 1.2m timber for the short sides
• Four corner posts, 75mm x 75mm, cut to about 350mm
• Roughly 32 exterior-grade screws, 150mm long
• Cardboard for the base, plus topsoil and compost to fill it

Ask your timber merchant to cut the boards to length. Most will do it for free or for a few pounds, and it saves you wrestling a handsaw in the drizzle.

Building the Frame

Choose a spot that gets six to eight hours of sun a day and sits within reach of a tap — you will water more than you expect. Clear the ground of weeds, then mark out your rectangle and check it is square by measuring the diagonals. If corner-to-corner measurements match, your frame will sit true.

• Knock each corner post into the ground with a lump hammer, leaving around 300mm standing proud.
• Fix the lower boards to the posts first, two screws per join, drilling pilot holes to stop the timber splitting.
• Check each side with a spirit level as you work round, then fit the upper boards the same way.
• Firm the frame down so it sits level, backfilling soil around the outside of the posts.

Building on paving? Skip the digging, use longer screws and fit internal metal corner brackets instead, so the frame simply sits on top.

Lining the Bed

There are two separate jobs here and they are often muddled. First, the base: lay overlapping sheets of cardboard, at least two layers thick, to smother grass and weeds without blocking worms or drainage. Do not line the base with plastic — water must be able to escape, or you will have a very expensive puddle.

Second, the inner sides. Some gardeners line them with heavy-duty polythene or offcuts of pond liner to slow the timber rotting; others prefer to let the wood breathe and accept a shorter lifespan. If you do line it, fix the material to the inner faces only, and never across the bottom.

Filling With Soil

Work out your volume before ordering anything. A bed of 1.2m x 2.4m at 300mm deep holds roughly 0.86 cubic metres — about six 70-litre bags for every 150mm of depth. Bulk bags work out far cheaper once you need more than 500 litres, and many suppliers will drop one on your drive.

A dependable mix, in roughly equal parts by volume, is:

• Topsoil or decent garden soil
• Peat-free multipurpose compost
• Well-rotted manure or homemade compost

Add it in layers, firming gently with your hands rather than stamping it down, and finish about 30mm below the rim so mulch and water stay where you put them.

Planting Up and Looking After It

Let the bed settle for a week, give it a thorough soak, then start planting. Space rows around 200mm apart and sow in blocks rather than long single lines — you will fit noticeably more in. A rough plan for the first year:

• Salads, radishes, herbs and spring onions for a quick early crop.
• Runner beans, courgettes and tomatoes once the last frost has passed.
• Carrots, beetroot and leeks for an autumn harvest.

Water deeply twice a week in dry spells rather than little and often, which only encourages shallow roots. Mulch with compost in late spring to hold moisture, net your brassicas against cabbage white butterflies, and move crops round the bed each year so pests and diseases do not build up. Top the soil up with compost every autumn, and that single weekend's build will keep you in vegetables for years.