windy coastal location may necessitate a different treatment compared to a sheltered inland site. Soil The quality of a garden's soil can have a significant influence on a garden's design and its subsequent success. Soil influences the availability of water and nutrients, the activity of soil micro-organisms, and temperature within the root zone, and thus may have a determining effect on the types of plants which will grow successfully in the garden. However, soils may be replaced or improved to make them more suitable. Traditionally, garden soil is improved by amendment, the process of adding beneficial materials to the native subsoil and particularly the topsoil. The added materials, which may consist of compost, peat, sand, mineral dust, or manure, among others, are mixed with the soil to the preferred depth. The amount and type of amendment may depend on many factors, including the amount of existing soil humus, the soil structure (clay, silt, sand, loam, etc.), the soil acidity/alkalinity, and the choice of plants to be grown. One source states that, "conditioning the soil thoroughly before planting enables the plants to establish themselves quickly and so play their part in the design." However, not all gardens are, or should be, amended in this manner, since many plants prefer an impoverished soil. In this case, poor soil is better than a rich soil that has been artificially enriched. Boundaries The design of a garden can be affected by the nature of its boundaries, both external and internal, and in turn the design can influence the boundaries, including via creation of new ones. Planting can be used to modify an existing boundary line by softening or widening it. Introducing internal boundaries can help divide or break up a garden into smaller areas. The main types of boundary within a garden are hedges, walls and fences. A hedge may be evergreen or deciduous, formal or informal, short or tall, depending on the style of the garden and purpose of the boundary. A wall has a strong foundation beneath it at all points, and is usually – but not always – built from brick, stone or concrete blocks. A fence differs from a wall in that it is anchored only at intervals, and is usually constructed using wood or metal (such as iron or wire mesh). Boundaries may be constructed for several reasons: to keep out livestock or intruders, to provide privacy, to create