In a hollow concrete block wall you can lay a wider strip foundation on the downhill or outer side of the wall and set in it L-shaped steel rods on which you can slot the blocks for extra reinforcement , then fill in the block cavities with concrete.

A tall wall over about 1.2m (4ft) high must incorporate supporting columns called ‘piers’ at each end, and also at intermediate positions along its length if it’s very long. You may, though, just want to include piers in a smaller wall purely for visual effect, where the wall breaks at each side of a flight of steps, or where the wall must support a heavy gate.

In a brickwork wall you should bond the piers into the structure for strength but in solid block walls you can simply tie a stack-bonded pier to the wall by setting galvanised expanded metal mesh in the horizontal mortar joints.

A wall of hollow concrete blocks can be similarly tied to a matching pier with special metal cramps, and the hollow cavities can then be filled with concrete for extra rigidity.

Another means of reinforcing an earth-retaining wall is to build it thicker at its base, stepping back the courses from the earth side to the final thickness at the top.

Long walls must also incorporate breaks in the bond called ‘movement joints’, which allow for seasonal expansion and contraction. Joints should run the full height of the wall and can be packed with a compressible material such as expanded polystyrene which can then be pointed with a weak mortar mix to conceal the gap. You should leave movement joints at every 3.6m (12ft) in brick walls and at every 1 8m (6ft) in block walls

Further Readings:

• How to Build a Wood Retaining Wall
• How to Plant a Hedge, Climber and Wall Plants

Bricks must be dense and durable to withstand the damp conditions to which your wall will be exposed, and can give a neat, formal appearance in a garden that has rigidly defined areas, such as lawn, patio and rockery Choose special quality or special engineering bricks which are quite impervious and ideal in wet surroundings. Ordinary quality or common bricks are far too porous and susceptible to frost damage, although if your wall’s going to be fairly small and in a sheltered situation you can use the more attractive second-hand ordinaries in conjunction with a water-proofing treatment.

The strength of a brick wall is in its bonding and the mortar mix used. A brick retaining wall, therefore, must be built a minimum of 225mm (9in) or one whole brick thick in a tough bond such as Flemish, English, or English Garden Wall bond for strength.

Concrete blocks, which are much larger than bricks and much lighter to handle enable you to build a high wall relatively quickly. They’re available either solid or with hollow cavities to take reinforcement. Make sure you choose dense quality blocks that are suitable for use underground.

If you don’t like the plain, functional look of concrete blocks you can clad the completed wall with a cement render, or coat it with a textured masonry paint. A rendered finish, though, is likely to crack eventually in damp conditions. Alternatively you can just use the blocks underground and continue the wall above ground with bricks. Concrete blocks should be laid in stretcher bond to give the strongest structure.

Decorative concrete walling blocks are suitable for low retaining walls; they’re available both in brick size and in the larger 215×440mm (9×18in) size, and usually have a split-stone or riven face for a more natural, softer look. They also come in a range of reds, greens, and buff tones for a more attractive finish. You should only use this type of block above ground. Use the same bonding patterns as bricks for a stronger structure.

A cast concrete retaining wall is tough and durable, but it has a drab, slab-like appearance and calls for the construction of sturdy timber formwork to mould the mix while it hardens. If you think you’ll need such a robust structure you can make it look a little more attractive by adding a pigment to the mix

You can even build a dry stone retaining wall for an unobtrusive cottage-style garden wall, although it’s not suitable for holding high banks or heavy soil weights. The irregular soil-filled gaps between each stone make ideal places for introducing creeping plants to mellow the overall look of the wall. In this type of wall, each stone must be tilted downwards into the bank, forming a slanted or ‘battered’ wall. This will increase the strength of the structure, and will also give it a much less formal appearance.

Naturally rot-resistant hardwoods or preservative-treated timber can be used to make a wooden earth retaining wall, or you can use it as cladding for a concrete or blockwork wall. Railway sleepers, for instance, which you can often buy from specialist suppliers, can be used to make sturdy retaining walls if you pile them on top of each other, or stick them in the ground vertically, and support them with steel rods or stout fence posts set in concrete foundations. You could even stack concrete or wooden fence posts in this fashion, or in a dove-tailed design, to leave small soil-filled gaps between each post for planting.

Further Readings:

• How to Choose the Materials for Your Garden Walls and Fences
• How to Design a Family Garden

Hedging subjects can now be planted at almost any time of the year as they are grown and sold in containers. It is generally a bad idea to try and establish a hedge during the summer as you will have all kinds of watering problems to contend with, apart from which the purchase of container grown hedging is inordinately expensive compared with that of bare rooted stock purchased during the dormant season. Deciduous hedging is best planted during the winter, but broadleaved evergreens and conifers should be left until the spring.

Select plants that are well furnished to the ground and go for the smaller sizes as these are more manageable and easier to get estab­lished. Large plants seem to provide an instant barrier, but unless you are excep­tionally lucky they will tend to have naked lower parts and rarely fill out to make an impenetrable hedge. Plant between 30 cm and 50 cm (1 ft and 1 ft 8 in) apart depend­ing upon the habit of the subject, where space allows in an alternate triangular fashion. Naturally the closer the plants are set the more quickly the hedge will become serviceable. If time is not a serious consider­ation a good hedge can be made much more economically by spacing plants further apart and feeding them well to encourage rapid growth. Once successfully estab­lished, a young hedge requires considerable attention if it is to be an object of beauty in future years. It is always a mistake to let plants grow tall too quickly. Encourage dense bottom growth by keeping them low initially, otherwise they become top-heavy and unwieldy and can only be rectified by drastic pruning.

Further Readings:

• How to Maintain a Small Garden
• How to Design a Formal Garden

A modest form of built-in decoration is a simple coping placed on the top of the wall, often used to complement fine stone or brick. More of a feature can be made if tiles or slate are used to complement the fabric of the wall. Piers or columns are a means of creating a functional but decorative structure: they may be there primarily to support the wall, but they are also ornamental and can be used to break the monotony of a flat surface. Another way of decorating a wall is to create a small round or square window, which can be left as an open space or covered with a metal grill. This will allow a glimpse of the area beyond, encouraging the observer to explore further, while from a distance the feature will look like a picture hanging on the wall.

Fixed patterns and designs using different coloured bricks can be incorporated into the wall at the time of building, and certain bricks can be left slightly proud of the wall surface to form a raised pattern. A less subtle form of decoration is to use pierced concrete blocks in a geometric pattern. These can be used on their own or built on top of an existing low wall, their angular appearance used as an asset in a suitable, linear design, or softened by climbing plants.

Applied decoration does not need pre-planning and can be used to add variety to existing walls. Urns, balls, obelisks and finials all look effective placed on the tops of walls, and framing columns or piers next to gates or doorways can be highly decorative. A more creative approach is to attach items to the wall. These can be in the form of ready-made pieces of sculpture, such as decorative masks, or perhaps a few unique pieces found in an antique shop. Another possibility is to make a mosaic out of fragments of coloured tiles and porcelain embedded in cement.

None of these effects should be overdone or allowed to become too dominant; they need to be subtle in order to blend in well with the garden.