A well-drained soil is essential not only for successful plant growth but also where paths and walls are to be built. It is therefore important to consider the drainage of your whole plot, not simply with regard to the growing areas.
Few plants like a lot of water around their roots and in soil which is constantly wet the plants roots will remain near the surface or will start to rot. Wet soils are also cold, which retards plant growth. When drainage is inadequate, not only is air blocked from the plant roots but the general lack of air in the soil means that bacteria cannot live and the bacteria are a vital part of healthy soil.
It is in particular heavy clay soils which suffer from poor natural drainage; sandy or stony soils usually drain quite freely. However, where the topsoil is a stiff loam the subsoil may well be clayey and nonporous, preventing water from draining away completely.
The simplest way of testing your natural drainage is to dig a hole about 600 mm (2 ft) deep and watch what happens after heavy rain – or simply sill it with water. If the drainage is good, the water should disappear in 24 hours; if it is still there after 48 hours the drainage defiantly needs improving. However, before spending money on expensive pipe drainage, bear in mind too efficient a system will impoverish your soil as the plant nutrients will be leached out very easily. Try one of the several natural corrective methods first.
It is important for a gardener to know about the water table. This is the line under the topsoil or subsoil, depending on the depth of these layers, to which water standing in the earth’s crust rises. It is not a horizontal line but conforms roughly to the contours of the ground.
The water table generally rises and falls following wet and dry periods. If it stands about 900 mm (3 ft) below ground level it can be an asset, since water will be available to the deeper plant roots. However extreme fluctuations in the water table are a…