Why Soil Drainage is so Important
TREES, bushes and plants will not grow in waterlogged, and if excess moisture cannot get away because of an impermeable subsoil some form of drainage must be provided.
A simple test is to dig, in the winter, a hole 2 ft. deep; if water soon fills the cavity, then artificial drainage is required.
There are various ways of laying drains, and the layman would be well advised to ask a landscape architect, or perhaps the local authority surveyor, for advice on the most suitable method.
Land can be effectively drained by means of pipes laid below the soil. These pipes are obtainable in fixed lengths and may be either of earthenware, tile or permeable concrete. The lengths of earthenware piping are laid with an £ in. gap between their ends through which the water can seep. But the roots of trees sometimes grow through these gaps between the piping, so that after a time the drains may become completely blocked. This trouble can, however, usually be obviated if permeable concrete piping is used, as the lengths can be laid closer together.
SIZE OF DRAIN PIPES
The main drain, which should be of 6-in. diameter piping, should run the length of the land to be drained from the highest to the lowest part of the plot.
The side or branch drains, which are usually called feathers, are of 3-in. diameter piping, and are put in to meet the main drain at an angle of 60° in a herringbone pattern, but no two feathers should join both sides of the main drain at the same point.
Though the drains can be laid 3 ft. deep, in many cases they need be no more than 20 in. deep. The depth depends to a certain extent on where the impermeable layer of clay lies, and therefore where the water is held up.
Dig V-shaped trenches for the drain pipes. Lay the main drain first, and then the feathers. Never give a steep slope to the pipes, but incline them very slightly so that the slope is barely perceptible. To check that the pipes have the right fall, put pegs into the bottom of the trenches, and place a board across them with a spirit level laid on it.
The problem in many gardens is where to take the water when it runs down to the end of the drain.
Sometimes there is a ditch at the bottom of the garden into which the water can flow, but under modern building conditions, especially in towns, it is necessary to build a soakaway to accept the water.
A hole should be dug 4 to 5 ft. deep and about 4 ft. wide, and the sides should be loosely bricked to allow the water to seep through into the soil if necessary.
Fill the hole with coarse clinker or brick rubble.
Cover the drain pipes with rough clinker or broken bricks so as to allow the water to trickle through quickly. Alternatively, brushwood or a 6-in. thickness of heather, if this is available, can be laid over the pipes. Then put the soil back in the same order in which it was dug out, leaving the surface slightly raised to allow the soil to settle at the right level later on.
If drain pipes are not to be used, then drainage trenches can be dug. These trenches should be 2 ft. deep, the main trench being 1 ft. wide and running to the lowest part of the garden. The side trenches should be narrower and should run obliquely into the main trench. Fill the bottom 6 or 8 in. of all the trenches with large stones, big clinkers, brickbats or similar material through which the water can percolate.
TIME FOR WORK
Drainage work in the garden is better done in the winter when more time is available as there are few other gardening jobs to do, and the interference with growing plants will be at a minimum.