Raised beds can provide many benefits for the gardener. As well as adding interest to the garden they allow a wider range of plants to be grown on either difficult soils or those with an inappropriate pH as you can fill them with a suitable soil mix.
Raised beds can also reduce or even eliminate bending, and the improved drainage ensures the soil warms more rapidly in the spring, allowing the vegetable growing season to start earlier.
Materials vary considerably in cost and ease of construction. Items such as brick and stone are the most expensive but offer a permanent structure if bonded with mortar. For less ornate areas gravel boards are a cheap, easy-to-use alternative. Brick and stone beds require concrete footings if more than four courses high. These should be approximately 15cm (6in) deep and 30cm (12in) wide. Railway sleepers can be fixed into place by hammering metal rods into holes drilled vertically in each corner, or using heavy-duty staples and wire. Gravel boards can simply be screwed onto sunken corner posts.
Long vegetable beds are best orientated to run north to south for even sunlight levels. They should be roughly 1.2m (4ft) wide with a 45cm (18in) path in between for wheelbarrow access. Paths are best covered in carpet, gravel or similar material as they can become too compacted to hoe. Raised beds for ericaceous (lime-hating) plants are best lined with polythene to separate lime mortar from the roots.
Permanent structures on poorly-drained soils require drainage material in the base, which should be covered with a membrane material before filling to prevent clogging up.
The growing medium depends upon the plants being grown, although organic matter and grit are always useful additions. Once filled allow the soil to settle for two weeks before planting. Vegetable beds can simply have their base forked over before filling, adding organic matter to one spit's depth.