Whilst some plants may flower all summer, most cannot be depended upon for more than three weeks - and in the case of irises or peonies for even less than that. Consequently, foliage plants are essential elements in a garden scheme, and their inclusion makes a garden considerably more interesting.

A 'foliage plant' is not necessarily a non-flowering plant such as a fern; it can also be one whose impact, and thus its place in the garden, depends as much on its leaves as on its flowers. For example, Japanese aralia (Fatsia japonica), has striking flowers but even more striking and longer-lasting leaves.

Plant foliage can vary enormously in texture and form: from the dainty and frond-like to the huge and broad, from the sturdy and glossy to the fragile and matt. You will find leaves in every kind of green, as well as grey, blue, golden, bronze, white, purple and even black. Leaves can be speckled, edged or splashed with white, cream or gold, or even a number of different colours, such as the leaves of Ajuga reptans 'Tricolor'.

The range of texture, colour and form is so wide that it is possible to make attractive and unusual effects using leaves alone. Variegated leaves, for example, can be set against the denseness of single-colour foliage (say, of a background hedge) to lighten the appearance of a border.

Foliage is possibly most useful in balancing out contrasting flower colours; it can be used to guide the eye to a transition from warm to cool colours, or to rescue a brightly coloured flower grouping from brashness. Foliage can also act as a repeating theme to bring together a border scheme and can soften the harsh rawness of new landscaping far more effectively than flowers.

Evergreens (and 'evergreys') give energy to what would otherwise be a predominantly dull and brown winter garden, as well as providing an effective background for more delicate perennials in summer. Most deciduous and many evergreen leaves also change colour during the course of the year. For example, many of the yellow-leaved conifers, which are insignificant, even a little drab in the summer, gain in brightness when the autumn comes. The colour of the new leaves of pieris, photinias and many rhododendrons and roses also often differs dramatically from that of the mature foliage.

Whilst foliage is one of the most important aspects of the garden, do bear in mind that it can occasionally be a negative feature. For example, slug-chewed hosta leaves are inclined to be conspicuous, and autumn-flowering colchium bulbs have large, fleshy strap leaves in the spring.