Raised beds

Raised beds are a great way of growing a wide range of plants, and are particularly popular for growing fruit and vegetables. They are a good way of boosting drainage and can be used to introduce a different soil type to your garden. Raised beds are also a useful way to garden if you have restricted mobility, as they reduce the need to bend.

Raised vegetable beds. Credit: RHS Advisory.

Quick facts

Rasised beds are good for:

  • Improving drainage
  • Increasing soil temperature
  • Improving access
  • Growing plants in a different soil type

Suitable for...

You can grow almost any plants in raised beds, try the following:

  • Soft fruits, such as strawberries, currants, raspberries and blackberries
  • Vegetables, almost any vegetable can be grown in raised beds
  • Herbaceous perennials, raised beds are a good idea for establishing a cutting garden for cut flowers
  • Alpines, ideal for alpines that relish good drainage
  • Small trees and shrubs, depending on how big your beds are, you may be able to grow some smaller trees and shrubs
  • Ericaceous or lime hating plants, by filling beds with acid soil lime-hating plants such as heathers and rhododendrons may be grown in areas of alkaline soil

Raised beds can be used to:

  • Improve drainage: Soil is raised above the surrounding ground level. However, this can be disadvantage in droughts as more watering may be needed
  • Increase soil temperature: Soil is raised beds is better drained, so warms up faster in spring
  • Enhance root health: Filling the beds with good topsoil enriched with fertiliser and organic matter gives excellent root zone conditions
  • Improve ease of management: Raised beds have a bigger soil volume than containers, so are easier to manage with watering
  • Match the soil to the plant: By filling raised beds with acid soil, for example, ericaceous (lime-hating) plants can be grown even where the underlying soil is alkaline
  • Improve ease of access: Raised beds are easier to manage for gardeners with mobility problems

Building raised beds: getting started

Although raised beds can be built at any time, most gardeners find it convenient to build them in winter, as long as the soil is not too wet or frozen. Where winter waterlogging is a problem, build raised beds in late summer. When building raised beds, the following points need to be considered:

  • Firstly, define how big your raised bed needs to be, and where you need it
  • Walking or stepping on raised beds is best avoided, so go for widths of less than 1.5m to allow access from the sides
  • Avoid long runs of beds so that people are not tempted to step on them to get to the other side
  • Pathways should be wide enough to wheel a barrow or accommodate special needs such as wheelchairs; 30cm (1ft) is the minimum width for walking and 45cm (18in) the minimum width for wheelbarrows
  • Consider the materials: timber is cheap, but even when treated is the least long-lasting; sleepers are long-lasting but costly, bulky and difficult to cut; masonry is costly but permanent. Alternatives include recycled plastic ‘timber’ lookalikes
  • Small scale projects might be accomplished using a ready-made kit

Building raised beds: construction

  • Clear the site of existing vegetation and level as required
  • Mark out the beds with stakes and string, and check the levels
  • For all but masonry walls, insert retaining stakes (5 x 5cm or 2 x 2in timber is suitable), at the corners and then at every 1.5m (5ft), sunk 30-45cm (12-18in) into the soil to support the sides
  • Attach the sides to the retaining stakes with nails or screws (screws are better for avoiding splitting)
  • Once the sides are in place, cultivate and enrich the underlying soil with organic matter
  • For beds deeper than 50cm (20in), remove the underlying topsoil (for use later in filling up the bed) and replace with subsoil, rubble or old inverted turves. Then replace the topsoil, enriched with organic matter (such as well rotted compost or manure) and fertiliser, firming in layers to prevent undue settling
  • Where the topsoil is unsuitable for the crop to be grown, leave it in place, but simply loosen it and fill up the bed with fresh imported soil of the correct type

Top tips

  • To save cost, use soil scooped from paths to fill beds, and fill paths with bark, gravel or other paving materials
  • Bury any turf removed in making the beds in the lower levels of soil in the bed to enrich the soil as it decays
  • When building raised beds on top of hard surfaces, ensure a depth of at least 45cm (18in), but ideally 60cm (2ft), so that plants can root deeply. This will reduce their watering needs

Problems

Plants in raised beds can suffer more quickly and more severely from drought due to improved drainage, so keep an eye on watering needs.

Modern wood treatments do not contain potentially harmful heavy metals, so are safe to use. If in doubt, line the inside of the bed with polythene.

New railway sleepers may contain creosote that should not be used where skin contact is a possibility. Creosote is thought to have dissipated from older sleepers, and these may be used without concern about skin contact.

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