Retaining walls | Drystone walls | Balustrades and rails
Walls at the boundaries of the garden delimit the extent of the garden but they also provide privacy and security. These will be the highest walls in the garden, about 1.8 metres in the back garden; about one metre for front gardens.
Usually made of concrete, less often of stone or brick construction, boundary walls are generally regarded as a gardening liability. However, they can add considerably to the usable space in the garden when their vertical area is taken into account. This is especially true of enclosed town gardens. Very interesting schemes using climbing plants and trellis work can be created.
Retaining walls hold back an earthen bank. They must be constructed properly with drainage holes every two metres and they must have a damp-proof-course at the back to prevent water seepage and structural deterioration. If they are more than one metre high, they might need reinforcing steel – ordinary blocks are not strong enough on their own – and an architect or engineer should be consulted.
Retaining walls define the area of ground that they support, separating it from other parts of the garden. Plants growing in the retained ground will be raised above the neighbouring area and this focuses attention on them.
However, plants grown at a retaining wall must not be of upright shape because they will look isolated. Some trailing plants to tumble over the retaining wall should always be used to link the raised plants with the rest of the garden.
A drystone wall is made without mortar holding the stones together. In practice, some mortar is often used, or soil in place of mortar, but it is kept hidden at the back of the stones. Drystone walls used in gardens are rarely two-sided; they are usually used as low retaining walls to front a terrace.
Because they have little inherent strength, no heavy loading should be placed on drystone walls, nor should they be built higher than one metre. They should always be built with a slope back towards the soil face, and filled behind with rammed earth to stabilise them.
Balustrades and rails
Where there is a change of level at the edge of a terrace, even quite a small drop, balustrading or rails can be considered, both for safety and decorative value. A balustrade is a concrete or stone coping supported by small columns, called balusters. Rails can be of any material, concrete, timber or metal.
They have the advantage over a solid wall of being open, creating less enclosure. Balustrade gives a formal, somewhat old-fashioned feel to a terrace; rails are more modern, especially metal. Timber rails, especially peeled rustic poles, are suitable for natural gardens.