Dealing with Poor Drainage

Drainage solutions
Often, a badly drained garden can be improved markedly by incorporating generous amounts of compost. Raising the garden beds, ideally by at least 22 cm, allows the root zone of most vegetables to grow in well-drained conditions regardless of the soil quality below, and the raised beds warm up more rapidly in spring. Digging, particularly double digging – which breaks up the hard pan, the subsurface layer of impervious soil – can also improve drainage. One or two trial holes will show whether such a layer exists. But while double digging is a good remedy, there is a slightly less laborious alternative. Choose a time when the soil is fairly dry, and dig it over to a spade’s depth. As you complete each row of digging, work along the bottom of the trench with a fork, driving it in to its full depth and levering it back so that the soil is lifted and fractures. You may need a pickaxe or mattock to break the hard pan. Do not try to turn the layer of subsoil beneath the pan. Just push the fork in, move it until the soil begins to give, then pull it out. In the worst cases, you may need to install underground drains before attempting to grow anything.

Pipe drains
If waterlogging occurs on heavy or low-lying land and there’s nowhere for the water to go, then pipe drains are probably the only answer. This is worth attempting only when the trouble is really serious and if there is a ditch into which the pipes can empty. If there isn’t a ditch, you’ll need to dig a soakaway – a large pit filled with stones or hardcore. Laying drains is heavy, specialist work, and you may want to hire someone to help you. If you decide to lay pipe drains, you can purchase them from builders’ or agricultural suppliers. For gardens, choose porous flexible plastic pipes or clay pipes; they should have an interior diameter of 50 or 75 mm. The pipe drain leads to the ditch or soakaway. First, lay 3 cm of gravel as a base in a deep trench that slopes
gently towards the ditch or soakaway; a drop of not less than 30 cm in 30 m is sufficient. Lay porous clay pipes end to end on the gravel base, setting the pipes with their ends about 2 mm apart so that water can enter from the surrounding soil. Alternatively, lay a single length of porous plastic pipe on the gravel base. Then cover with a further layer of gravel. Cover this with fine mesh or agricultural fl eece before filling with a 25–30 cm layer of topsoil.

Raised beds
An easier solution, particularly for a small area, is to make raised beds. They are ideal in areas with heavy seasonal rainfall, too. They also allow you to grow a wide range of plants when your garden has problem soil because you can fill the beds with whatever soil mix you choose. You can make a permanent raised bed with sides of bricks, stone blocks or railway sleepers, or a less expensive and permanent structure using planks of wood or corrugated iron. Make the bed 30–60 cm high. The ideal size is 1.2 m wide, which allows you to work the bed without walking on the soil. Allow a minimum of a 45 cm path in between beds for wheelbarrow access. Put a layer of rubble in the base to help drainage, then fill with soil. Let the soil settle for two weeks before planting. Once built, all you need do is fork over the beds each year and top them up with organic matter. No-dig gardens have similar benefits.