Dealing with clay soils

FC Architects
Feb 9
2 min read

When working in London and the southeast you will always encounter clay soils and for many of us this can create headaches. From trying to achieve a picturesque lawn to pouring foundations, clay soils can become a difficult obstacle to overcome.

In this blog I want to tackle clay soils in our domestic gardens as a result of my own experiences in trying to renovate a friend's garden. This involved extending a patio and trying to grow an acceptable lawn. We carried out the work ourselves to really understand the problems in getting a good lawn with dense clay soils. We made a few mistakes and tried many things that didn't work out, and it's still ongoing! Hopefully we will find a solution so please follow and let us know your thoughts!

The property is one of those generic, mass, new-build developments that garner a bad reputation for build quality. This house isn't so bad, but the garden lacked any kind of attention.

Through a trial pit we discovered a depth of over 600mm of very dense, clay soil - so dense it wouldn't let water pass through and easily formed a solid shape when compressed. The builders had laid turf which simply died away in most places due to a lack of root penetration, no drainage, and no oxygen in the soil. Grass needs all these to flourish and the density of the clay meant there were no gaps for this to happen.

The lack of drainage also mean during the winter months the garden would become sodden and boggy, remaining completely unusable for most of the year. In the warmer months, the compacted ground would become rock-solid and prevent root penetration, not to mention the unevenness of the land.

We started with trying a soakaway and dug down until we thought we had reached sandy, more free draining soil - about 700mm down. we lined this and filled with gravel. The plan was to alleviate surface water run-off rather than below ground water because we knew the density of the clay would never allow it.

Unfortunately, this simply didn't drain fast enough to help with surface water. We decided to extend the patio over an area of ground which was always boggy as the garden sloped towards this part of the garden. This would make the area useful all year round. Surface drainage would be via a gravel strip along the edge of the house (this is where most of the garden water wet to in any case as it struggled to penetrate the clay).