A rock garden should be constructed in an open sunny and well-drained position in the garden. No matter what size or shape it takes a rock garden must embrace the principles of a moraine. It should not be a mound of soil with rocks placed indiscriminately on it, but a collection of free-draining debris mixed with a gritty soil that is distributed through and around a rocky structure. Such an arrangement provides the perfect conditions for growing a wide array of fascinating mountain-dwelling plants.

There are a number of different stones that are readily available for rock garden construction. Sandstone, limestone, and granite are amongst the favorites, although most gardeners concede that a stone that is natural to the locality generally fits into the garden best of all. It is also less expensive because the transport costs have not been so great in getting it to the garden center. While it is possible to gather rocks that occur naturally, make sure that any possible conservation issues have been checked first. There may appear to be plenty of rocks scattered around the countryside locally, but their removal may not always be prudent or legal.

The rocks that are to form the base of the rock garden should first be selected and placed in position to create what almost amounts to a "retaining wall". This outlines the contours of the feature. As far as possible a rock garden should look as if it is growing out of the landscape rather than it is sitting on it. There are many gardens that are homes to heaps of soil with rocks awkwardly protruding from them. Such rock gardens are generally referred to by professionals as "currant buns", and are both visually unappealing and poor homes for most rock garden plants.

In order to create a natural-looking rock garden select a rock to provide the focal point. This is generally one of the largest rocks and is known as the key stone. It exposes at least two faces, often more, and it is from this that the remainder of the rocky outcrop develops. When placing rocks make sure that the strata runs in the same direction. If there are slight color variations create sufficient space between the rocks to allow for liberal planting. Two rocks of slightly variable color, which are separated by plant foliage, are no longer noticeably different.

Once the basal stones of the rock garden have been laid the area between should be filled with a mixture of about two thirds of broken stone or brick and one-third gritty soil. Having laid the base, filled the cavities, and generally formed a solid plateau, further stones can be lifted into position and the process repeated until the formation is of the desired shape and height. When completed, pockets between rocks that are to provide homes for plants with specialized requirements can be excavated and suitable compost introduced.

Philip Swindells has over 40 years gardening experience. A former botanical garden curator and an international horticultural consultant, he has worked extensively overseas. The Author of more than 50 gardening books, he has been awarded a Quill and Trowel Award by the Garden Writers