Constructing your garden. Drainage
Few small gardens need a full drainage system but where drainage is necessary it will be obvious, for the garden, or parts of it, will be wet underfoot for long periods. It is possible, however, that your rite is on low-lying ground and, while dry in summer, the water table will rise in winter to make the area wet again. The natural vegetation will indicate this – rushy grasses and little else.
By far the most likely cause of dampness, especially in a new garden, is a layer of clay from excavations that has been dumped and spread on site by the house builder. Often he disguises this with a thin layer of topsoil but the clay soon becomes an impervious layer that prevents drainage. Break this layer and the water will disperse.
Dig an inspection hole, a metre square and a metre deep, if you are in any doubt about the need to drain a particular area. In this way you will be able to see the soil profile and know how much topsoil and subsoil there is. After rain, you will also see how quickly water drains away. It is possible that your hale will fill with water when I is not raining, indicating that you have reached the water table. However, if you do at so shallow a depth your house will have needed special foundations and you are probably aware of this from a surveyor's report.
If the site is on natural clay, you have no alternative but to replace it with fertile topsoil. However, a soil with a proportion of clay may have become consolidated by heavy machinery working on it. Often this can be greatly improved by cultivating the surface to break-up the clay deposits that have been consolidated.
If your site really does need draining, you will have to install an underground system with pipes of either clay or flexible plastic. These are laid to a pattern according to the site, with feeder runs to the main outlet pipe running to a neighbouring ditch or to the surface water drainage system of the house. Never connect a garden drainage system to the main drainage system. In the United Kingdom this, in fact, is illegal.
The depth of the drainage runs, and their proximity to each other, will depend on the consistency and composition of the soil. It is important to realise that to overdrain a site is as pointless as trying to garden on one that is wet, for you are facilitating the rapid escape of all the essential minerals which are held in soluble form and feed the plants' roots.
The kind of drainage that a garden is likely need deals with only a small area, which, for a number of reasons, may have standing water on it after rain. To drain this ay only need a simple pipe run to a soakaway, dug within the site. A soakaway is a hole, a metre square and at least a metre deep, which if filled with rubble. It will act as a reservoir to hold drainage water, allowing it to disperse gradually. Such a soakaway should be sited under areas that will later be planted and at a distance from the house. The lifespan of a soakaway may be five years or so, but this again will depend on the soil.
Soakaways can also drain areas at the base of contoured mounds or be sited along the edge of an area of paving, which has been laid to fall to it.
By far the most likely cause of dampness, especially in a new garden, is a layer of clay from excavations that has been dumped and spread on site by the house builder. Often he disguises this with a thin layer of topsoil but the clay soon becomes an impervious layer that prevents drainage. Break this layer and the water will disperse.
Dig an inspection hole, a metre square and a metre deep, if you are in any doubt about the need to drain a particular area. In this way you will be able to see the soil profile and know how much topsoil and subsoil there is. After rain, you will also see how quickly water drains away. It is possible that your hale will fill with water when I is not raining, indicating that you have reached the water table. However, if you do at so shallow a depth your house will have needed special foundations and you are probably aware of this from a surveyor's report.
If the site is on natural clay, you have no alternative but to replace it with fertile topsoil. However, a soil with a proportion of clay may have become consolidated by heavy machinery working on it. Often this can be greatly improved by cultivating the surface to break-up the clay deposits that have been consolidated.
If your site really does need draining, you will have to install an underground system with pipes of either clay or flexible plastic. These are laid to a pattern according to the site, with feeder runs to the main outlet pipe running to a neighbouring ditch or to the surface water drainage system of the house. Never connect a garden drainage system to the main drainage system. In the United Kingdom this, in fact, is illegal.
The depth of the drainage runs, and their proximity to each other, will depend on the consistency and composition of the soil. It is important to realise that to overdrain a site is as pointless as trying to garden on one that is wet, for you are facilitating the rapid escape of all the essential minerals which are held in soluble form and feed the plants' roots.
The kind of drainage that a garden is likely need deals with only a small area, which, for a number of reasons, may have standing water on it after rain. To drain this ay only need a simple pipe run to a soakaway, dug within the site. A soakaway is a hole, a metre square and at least a metre deep, which if filled with rubble. It will act as a reservoir to hold drainage water, allowing it to disperse gradually. Such a soakaway should be sited under areas that will later be planted and at a distance from the house. The lifespan of a soakaway may be five years or so, but this again will depend on the soil.
Soakaways can also drain areas at the base of contoured mounds or be sited along the edge of an area of paving, which has been laid to fall to it.
