Materials for Raised Planting Beds

Raised beds may be constructed using a variety of materials, such as:

mortared bricks
concrete walling blocks
unmortared natural stone
railway sleepers
gravel boards

The choice of material for a raised bed will usually depend on the overall style of the garden and house. For example, a bed built next to a brick-built house will almost invariably also be built of brick to blend in with the design. However, contrasts are also welcome in the garden, so a raised bed made from railway sleepers could provide an interesting element on a terrace built from brick and slabs.

Brick Beds

Raised beds may be built using frost-proof bricks; ordinary house bricks may be unsuitable, so check with your supplier before buying. Bricks can be laid in a single layer, 45 cm (18 in) high, although a double layer should be used if you want to be able to sit on the edge. Always leave some joints open at the bottom of the wall, just above ground level for drainage.

If you intend to grow plants that require acidic soil, you will need to line the bed with several coats of a bitumen-based paint or a water-proof butyl rubber liner to prevent the lime in the mortar leaching into the soil.

Concrete Block Beds

Concrete blocks can be an excellent material for raised beds, especially if they have been used elsewhere in the garden. Although the blocks are generally too large to create curved walls, they are ideal for creating rectangular beds. Concrete beds may be constructed in a similar way to brick beds.

Stone

Natural un-mortared stones may be used to build low beds (less than 60 cm or 24 in), using the technique for dry-stone walls. Higher walls will need to be mortared to keep the stones firmly in place.

Sleepers

Railway sleepers are particularly good for low raised beds. Their heavy weight makes them extremely stable, and as a result, no concrete footings are needed. The sleepers may be laid horizontally in a running bond using multiples of full or half sleeper lengths. Any beds higher than two sleepers will need reinforcement such as steel rods or stakes to hold them together securely.

Alternatively, sleeper beds may be built using shorter lengths set vertically into the ground. They should be sunk into the ground to about half their depth to provide a firm and secure fixing. The tops can either be set flush in a horizontal line, or staggered slightly to create a sense of movement and flow.

Sleepers may be impregnated with a wood preservative that is toxic to plants, so ask the supplier for ones that have not been treated in this way. Alternatively, line the bed with a layer of polythene to prevent the toxic chemicals from getting into the soil.