Garden Drainage: Improving soils
Having gone to the trouble and expense of providing a means of getting rid of surplus water, you should focus your attention on increasing fertility and improving thestructure so you can get the most from your garden.
In addition to the actual cultivation of the soil, methods of improving naturally slow-draining soils are: incorporating manure, garden, or other suitable ; liming and subsoiling; incorporating aggregates; and exposing the soil to frost.
The addition of organic matter helps to aerate and improve the structure of silt and clay soils, and increases the moisture-retaining power of sandy and gravelly soils.
Liming improves land in a number of ways: by sweetening acid soils, encouraging beneficial bacteria, and by improving the crumb structure of clay soils. The application rate depends on the type of soil, its pH level (acidity or alkalinity), and the crops to be grown in it.
Gypsum (calcium sulphate) is also useful as a soil improver, particularly on heavy clay soils, as it produces a good crumb structure encouraging excellent drainage. Because it is neutral in reaction, it is useful for adding to soils which are already alkaline, and is particularly helpful on heavy clay soils which have been flooded with salt water. An average dressing for a heavy soil is 240 g per sq m (8 oz per sq yd).
Subsoiling involves loosening up the subsoil, which should be found to begin at roughly three spade’s depths (about 1 m or 3’), once every two or three years, using a spade or fork.
A hardpan is a hard layer of either compacted soil or a layer of mineral which can prevent or at least impede drainage and root growth. A compacted layer may be formed by cultivating the ground to the same depth year after year. A mineral layer can occur for a number of reasons, but occurs more frequently on poorly drained soils.
The addition of clean river sand, gravel, or washed clinkers all help to lighten and open up heavy land.
In autumn before the hardest winter frosts arrive, dig the soil into ridges, to expose the maximum surface area to the action of frost and wind, which will break up the lumps of soil. This is particularly effective with clay soils, and the beneficial effects last for some considerable time.
Sowingcrops such as and digging them in before they run to seed will also improve the land.
In very wet, poor-draining areas, crops can be grown on ridges or inon heavy land, when growing plants on the fiat would be out of the question.
Drainage and irrigation
As explained earlier, soils vary in the rate at which water drains through them; clay and sandy soils are extremes, behaving very differently from each other.
An example will serve to illustrate this point: a certain amount of water took several days to drain completely through a layer of clay loam, but the same amount took only three minutes to drain through an equivalent depth of sandy soil.
If you garden on soil that is slow to drain, you can try watering crops such asby sinking a small plant pot up to the rim in the soil near the roots of each plant. Make sure that the pot has a drainage hole or holes at the bottom. The water will drain at a steady rate into the area where it is most needed—among the roots.
Sheet irrigation involves levelling the land, and then by a series of ditches and ridges alternately flooding and draining it. The name of this method is derived from the fact that, effectively, a thin sheet of water is allowed to flow over the land.
Furrow or ditch irrigation consists of diverting water into furrows tosown or planted on ridges or in adjoining furrows. This works well with crops, such as , that require large amounts of water. The quality of the water is most important; the use of salt water should be avoided, also water from land with diseased crops must not be used. Water for sheet and furrow methods is most easily supplied from higher ground, but if this is not possible, you must install a small pump, which may well prove very expensive.