Raised Bed vs Ground Growing: Which Suits a Scottish Garden

A raised bed pays off where the soil is poor, heavy or waterlogged, and for easier access and an earlier spring start. It costs you money, more watering and a smaller growing area for the same budget, and it does not fix a site that does not drain. On decent soil, or on anything allotment-sized, growing in the ground is cheaper and does as well.

What a raised bed gives you

Warmer spring soil. Raised beds increase soil temperature in spring, which gets vegetables off to an early start (RHS). That helps in a short, cool Scottish season, though nobody has put a figure on how many days it saves. The trade-off is likely rather than measured: a raised bed has more of its surface exposed to the air, so on a still, frosty night it may lose heat faster than flush ground, and a framed bed standing proud of the ground may catch more wind on an exposed coastal or upland site.

Drainage and your own soil. You fill the bed with a fertile, free-drainingSoil that lets water pass through quickly rather than pooling, so roots aren't sitting in wet ground after rain. Full definition → mix, which suits garden soil that is heavy and prone to waterlogging, and on peaty, acid or stony ground it lets you choose the soil your crops root in. Raised beds are often used for rhubarb and asparagus, which dislike sitting wet over winter. The RHS fill mix is three parts organic matter, two parts sharp sand and seven parts topsoil. For a deep bed on poor ground, remove the turf and topsoil and replace it with rubble or subsoil to improve drainage and cut the amount of good soil you need. That helps water leave the base a little faster, but it is a partial improvement, not a substitute for draining the site.

Reach and access. Keep a bed less than 1.5m (5ft) wide, so you can reach the centre without standing on the soil. Raised beds are more accessible for gardeners with restricted mobility, and they are easier to manage than open ground because of their limited size. Working from paths around the bed also keeps foot traffic off the soil your plants root in, which matters most on clay that compacts underfoot. Site them in full sun, away from tree shade, and run long beds north to south for even light.

Depth. 30cm (1ft) is enough for dwarf bulbs, salad leaves and strawberries, but most plants need 45cm (18in) or more.

What it costs you

Money. You pay for a frame and enough soil to fill it, and the price of timber edging has gone through the roof (RHS). Pallet collars, scaffold boards, bricks, stone and recycled plastic are alternatives; raised bed materials compared sets out the options. Fill mostly with topsoil, because soil does not break down and slump in a few seasons the way compost does. Digging the ground you already have costs only the compost or manure you choose to add. Mounding soil without sides is a cheaper way to raise the surface, for labour alone, at the expense of neat edges and control of depth; see no-dig gardening on heavy clay. Frames that stand in wet ground will also stay wet on the outside, whatever is happening inside.

Water. This is the cost people forget. Plants in raised beds tend to suffer more quickly and more severely from drought than plants in the garden soil, and raised beds dry out quicker than ground-level soil, so install water butts at the same time (RHS) and mulchA layer of material spread over the soil around plants to suppress weeds, retain moisture, and improve soil structure as it breaks down. Full definition → the surface to conserve moisture. Setting up a water butt covers sizing and set-up. Rainfall varies widely, so drainage is likely to matter more in the wetter west than in the drier east, and you may be watering more often in the east: under 700mm a year on the East Lothian, Fife and Moray Firth coasts, under 1,000mm on the Ayrshire and Dumfries and Galloway coasts, and over 3,500mm over the higher parts of the west Highlands (Met Office).

Growing area. Part of the budget goes into walls and fill, so you get less growing space for the money than from the same ground. At allotment scale the cost of building and filling several beds climbs much faster than digging what is already there.

Slugs. Do not count on a raised bed to keep slugs out. Slugs and snails are well suited to the damp, mild UK climate, so pressure stays high in Scotland, and a bed's height is unlikely to protect a crop beyond a modest edge. An RHS study found no reduction in slug damage from copper tape, bark mulch, eggshells, sharp grit or wool pellets.

What a raised bed does not fix

Lifting the growing zone does not change what is underneath. If the ground under and around the bed is waterlogged, as on heavy clay or gley that stays wet for long stretches, the bed deals with the surface while the same blocked drainage sits below, and roots that reach the base meet the same wet layer. A raised bed can be part of the answer on a wet site, with rubble or subsoil at the base of a deep bed, but not the whole answer. For what fixing the site takes, see improving clay soil.

When growing in the ground wins

The RHS advice is that raised beds are really needed only where garden soil is waterlogged, and that you can grow vegetables just as well in the ground.

• Decent soil already. On workable loam a raised bed buys little, and you pay for the frame and fill.
• Large areas. Raised beds multiply material costs, while improving the ground costs compost and time.
• Deep-rooted crops. Parsnips need deep, light soil that drains readily, and stony, shallow or heavy soil makes long-rooted carrots and parsnips fork and distort. Deep ground gives that for nothing, while a bed needs filling to 45cm or more. Short-rooted varieties suit shallow or stony ground, and carrots also grow well in containers (RHS).
• No drainage problem. If water was never the issue, a raised bed has little to solve.

Raised bed and ground growing compared

Which to choose

Build a raised bed if the soil is poor or heavy and improving it in place would take too long, if you need easier access, or if an earlier start matters more than extra watering, and the area is small enough to afford. Make sure the underlying drainage is fine or fixed separately.

Grow in the ground if the soil is loam or improved clay, the area is large, you want long root crops and the ground is deep and fairly stone-free, or you have no drainage problem and budget matters more than convenience. On a waterlogged clay site, see improving clay soil and no-dig gardening on heavy clay.

Common questions

Sources