Dear Sibe,

Recently our garden was flooded about three quarters way up and our grassed area always seems to be waterlogged, even when the weather has been mainly dry. The garden has a slope to it but there doesn't seem to be any difference in the wetness. We also have a problem when it comes to cutting the grass, as soon as you walk on it, it ends up looking like a mud bath. Please help!

Thanks,

Tracy

Our Gardening Expert replies:

Hi Tracy,

I think the first thing that you should establish is whether this was a one-off flooding or a regular event when there is heavy rain. A good way is to ask neighbours who have lived nearby for a long time or know the area well. If it seems this has not happened very frequently, there may be a problem with a recently blocked land drain in the property behind yours. The Local Authority may be able to help or may at least know if drains have been laid there. Or you could approach the land owner on the flooded side to see if there is anything they can do.

If such floods seem likely to happen again, there is little you can do but try to plan for this, even though the next flood may be years away. Firstly, it may be sensible to move the shed higher up the garden or at least to reposition it on a raised base. You could then plant the lowest area with suitable plants that would put up with occasional flooding. I am sure you'll find that the grass itself will recover in time but there are many other plants which would relish the occasional flood and grow really well in such a position.

As for as the general wetness of the garden, a gentle slope is of little use on a heavy clay soil, but there are things you can do to make this area more useable.

Firstly, it would be a good idea to dig a few really deep holes to investigate what is under the clay soil. You may well come across an area of compacted subsoil (lighter in colour, often of a marly appearance and quite dense) which is stopping water freely draining away.

If this is not the case and the bottom of the hole is quite dry, then it is the clay itself which is impeding drainage. The best treatment for this in a heavily planted area is simply to add masses of well rotted compost, manure, composted straw etc and to dig in lots of grit. A few years digging in large amounts of these materials will result in a very fertile soil as clay soils are high in nutrients. You could install slightly raised beds (6in (15cm) to 12in (30cm) high would be enough) that are filled with freely draining soil (ie the humus and grit mixed in with your clay soil). Reclaimed railway sleepers or brick/stone can be used for the walls.

If the bottom of the hole is permanently wet it is likely that you simply have a high water table and there is nothing you can do about this!

In the optimistic assumption that the hole is dry at the bottom then you could install a drainage system underneath your lawn. These work well on clay soils. Plastic perforated land drains laid at the bottom of a rubble-filled trench, with a gentle slope into a large soakaway or some other outlet, are quite possible to install yourself with some guidance and a good trenching spade.

Happy gardening,

Sibe

For more practical tips, see Lawn Maintenance and Organic Gardening.