When building raised beds using bricks you should always choose frost-proof bricks. A half-brick wall is usually strong enough. The most common shapes of raised beds built with bricks are rectangular and circular. A large, rectangular brick bed is easy to build but it may look unimaginative. It will better to create a number of smaller, linked beds at different heights. This will create a more visually stimulating feature, as well as a circular raised bed.
For building a rectangular bed you need first to prepare the footing at a depth that allows the first course of bricks to lie below ground level. After the footing is set, use a masonry mortar mix to lay the courses of bricks. Lay whole bricks at right angles to form the corners.
For a circular bed, the bricks should ideally be cut to give a smooth curve but it is possible to use full bricks also. Before starting to build the bed lay the bricks loosely with a circumference large enough to ensure that there are no wide gaps at the edge. Prepare the footing and after this is set lay the bricks so that they almost touch on the inside edge of the wall. Then use wedges of mortar to fill the gaps on the outer face. Stagger the courses as with a conventional bond and use half bricks for the final course to give a better curve.
If you are going to grow in your raised beds plants that require acid soil, you should line the inside of the walls, after they are completed, with a butyl rubber liner or several coats of a waterproof, bitumen-based paint. This will stop the lime from the mortar from leaching into the bed.
Concrete block beds
You can use concrete walling blocks to build raised beds. They are a good choice especially when matching materials have been used for other garden structures and surfaces. The concrete blocks may be too large for circular beds but they are ideal for rectangular ones. The building method is similar to the brick beds.
Raised beds may also be built using natural stone laid dry. They suit well for low and small beds. For a bed higher than about 60 cm it is best to mortar the stones securely in place. Even with a low bed it may be necessary to mortar the corners for stability. Either way you have to build the bed on a concrete footing or a foundation of rubble.
They are good choice to build the raised beds as they blend unobtrusively with most garden plants and surfaces. They are the ideal choice for large, low, raised beds but they are heavy and difficult to handle so you should not make the walls higher than three sleepers. Use a chainsaw to cut the sleepers to the needed length but use as much as possible full or half sleeper lengths to reduce the amount of sawing involved.
For this type of beds there is no need of a footing since the length and weight of the sleepers make them extremely stable. Just create a level surface using rammed gravel to lay them on then bond the sleepers like bricks. If you are going to build the bed laying more than two courses, then you should use metal rods driven into the ground to secure them in place. If the sleepers are already impregnated with bitumen or a wood preservative that is toxic to the plants then you should line the bed sides with a geotextile fabric, PVC or butyl liner.
Logs make attractive edgings for woodland-style beds and for very low, informal beds in a natural setting. For higher raised beds you should use logs of a uniform size and thickness. These may not be readily available and the corner joints are difficult to construct. If you are choosing to build this kind of raised bed than it might be a better idea to buy it as an easily assembled kit form.