Materials and detailing should be at the back of the designer's mind from the very start of a project, because it is through these that the mood and style of the garden can be conveyed, every bit as much as through the spatial arrangement and the planting.
Materials in traditional and modern usage - the power of association with regional traditions means that the location of at least some of these is obvious without any further information.
Materials have to be suited to the garden as well as to the local vernacular styles of building and construction, and for this reason I feel strongly about the use of plastics, glass and stainless steel in contemporary gardens - they are available everywhere, have an immutable appearance and do not reflect any traditions of building for many of the gardens they are used in.
For show gardens, where there is no context within which the garden exists, these materials offer a great opportunity to experiment with shapes and structures, and in a setting of modern architecture they are clearly more appropriate and have their place. If we want to use these modern fabrics in our designs then we should be pushing developers, planners and architects to build visually and spatially modern housing stock - housing that is not merely a tepid rehash of the sub-Arts and Crafts genre which has prevailed in the UK since the 1920s but which is not only well-suited to the needs of modern living but also offers a suitable backdrop for the contemporary garden.
It is possible, however to find modern materials and usages that can bridge the gap between a modern garden and period houses. Gentler surfaces, such as that offered by Cor-ten steel, for instance, are a halfway house between the modern and traditional - the modern material picks up the colours of earth and brick, and is a subtly changing presence as it weathers.
A tank in Cor-ten steel, with Bredon gravel terrace and crisp timber cladding: bridging the gap between traditional and modern.
The best materials to use in most gardens will be those which have a counterpart in the local architecture or which are established as the best suited for their purpose. In an exterior context we are talking about stone (limestone, flint, sandstone), brick, iron, timber, gravel and tile.
Using materials appropriate to the climate and building tradition of the area makes a design relevant - it will sit happily with the house it belongs to, and will be a far less jarring imposition in the landscape than if the materials are alien.
In city courtyards and gardens (in which the relationship of the local architecture to traditional forms and the landscape has already been stretched to breaking point by the urban surroundings) there is greater scope for the use of modern materials, but I feel that there are plenty of ways of creating an up-to-date look in gardens with traditional materials if these are handled creatively.
Think about the alignment and spacing of timber and stone, flush finishes placed next to unfinished surfaces, juxtapositions of the unexpected, combinations of materials exploited for their differing structural qualities: there is plenty of scope here for creating something unusual yet true to the vernacular traditions of a site. Ironwork set in Bredon gravel, timber of differing widths and spacings to clad fences or shelters, unplaned timber contrasted with highly finished render or tiling, decking planks interspersed with channels of gravel or grass - all these could (and do) bring traditional materials convincingly into contemporary exterior design, and are examples of the ongoing dialogue that a garden has with the surrounding landscape and with the people who create it.