Seeking Advice on the Right Subsoil for My London Garden

Ronald Robinson
5 months ago

Hi all,

I'm doing a gardening project in my London home and really need some advice regarding the best choice of subsoil. Here's a quick rundown:

I've dug a trench about 60 cm deep and 30 cm wide, totalling approximately 30 meters around the garden's perimeter to lay an electric cable for outdoor lighting. The existing subsoil was primarily clay-based, so I disposed of it, thinking it might be best to bring in a new, better-quality subsoil instead of trying to amend the clay.

The dilemma arose when I approached a few companies to purchase the new subsoil. While I initially believed that the British Standard (BS8601:2013) would be the obvious first choice, some suppliers advised against it, suggesting a free-draining alternative. It's worth noting that the price difference between the two is minimal, so this isn't a cost-related issue. They mention compaction as a primary concern with the BS option, which threw me for a loop.

So now I'm at a crossroads: do I stick with my initial inclination toward the BS8601:2013 Subsoil, or do I heed the advice of the professionals and opt for the free-draining alternative?

I'd greatly appreciate any insights or experiences anyone could share to help me make the best decision for my garden and achieve my ultimate goal of adding topsoil and lay fresh turf. Thanks in advance!

Comments (2)

  • Jonathan
    5 months ago
    last modified: 5 months ago

    Assuming your garden is about 30’deep and 40’ wide I think you have made a great start by removing about 5% of the offending clay. But the middle will still be clay and causing problems for the lawn. Personally I think you should hire a rotavator and use it to break up all the soil and mix in organic material such as manure or soil conditioner (rather than buying top soil). Clay tends to be alkali which helps you choose the plants you buy but if you have particular plants in mind there may be a recommended compost.

    Grass needs about 4” of reasonable soil and border planting at least 12”. So you have got off to a great start. I wonder if the trench is necessary- armoured cable should be buried deep but most modern lights use such low energy that you can have a socket on the side of the house and surface cable over the garden without fear of electrocution. Also given your garden size could it be worth raising the beds in order to gain height for privacy without intruding too much into the space?

  • PRO
    AGI Landscapes
    5 months ago

    Clay soil is mainly alkaline to neutral a 7-10ph level. If you are just looking to replace the subsoil in your trench, remember that this will just become a soggy trench as the water will not drain away as fast through the surrounding clay.

    If the top soil layer in the rest of the garden is of a suitable depth and reasonable for planting in, you could put a permeable membrane in the bottom of the trench and fill with clean 20mm gravel 6"-8" deep and cover it with the membrane, then add your subsoil and topsoil, this would then effectively become a soakaway for the rest of the garden.

    As for the type of subsoil its really up to you what you decide, just have a look at what is on offer before you buy and check it's not full of rubble, waste, weeds etc.

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