As well as offering protection from the elements, screens, whether natural or prefabricated, can be used to enclose the garden both vertically and horizontally, and to define axes and vistas. They give the garden form and, by concealing parts of it, make it more interesting, imparting an air of mystery and inviting exploration. On a slope they may be used to give a feeling of stability. Pergolas, walls and hedges all provide microclimates due to the shade they cast, the protection they give from the wind and, in the case of south-facing walls, the heat they give off as infrared radiation. [...]

Walls have certain advantage over hedges. They are built quickly and do not change their height or width with age. Since they have no roots, they do not interfere with the growth of plants at their foot and you can grow plants up them. Neither do they suffer from disease. In sum, you trade a high initial cost for low maintenance. [...]

Not only do hedges have a more natural feel, they serve as a refuge and resting place for birds. But while hedges are comparatively cheap and easy to start, slow-growing species, such as box, may take ten years to reach a reasonable height while fast-growing ones may need trimming several times a year. Most need watering and some need periodical spraying with insecticides.

Take care when planting a hedge along the edge of a terrace. If this has been properly made, the carefully fitted large blocks that form the face will be backed by as much as 1m/3ft of loose stones. Do not plant within 1.5m/5ft of the edge of the terrace, at very minimum, in order to avoid this band of stones. Moreover, cutting the top of a hedge along a terrace will be much easier if you can lean the ladder on the outside of the hedge with its feet on the top of the wall. Hedges should always be cut with a face that slopes inwards towards the top, to prevent the base dying and, on terrace edges, to avoid them overhanging the wall at the base in an ungainly fashion.