[Vaughan]

Hello members, my wife and I are building a house and starting a new garden near Uzès. We will be landscaping over summer 2014, and start planting in the Autumn. I believe the plot was cleared at one stage but appears to have reverted to Garigue over the last few years, with wild Cistus, Thyme etc. The soil is classic med garden material, thin topsoil of a few cms over rock. Conditions have been made worse by heavy machinery digging out the pool and foundations, and back filling a shallow slope between house and pool with the rocks and soil, probably 80 or 90% rock. I have read O. Filippi and note his advice about not importing topsoil, large planting bowls etc, but would this apply to our situation with so much rock? We have consulted a local nurseryman and landscaper and he recommends adding 20-40cms topsoil with some kind of membrane between the rock and topsoil. Instinctively this seems to go against Filippi's advice, but I would like MGS members opinions on this. I'm sure if we left the rock rubble as is, nature would find a solution and the Cistus and others would return. My best guess is a hybrid solution with some topsoil used for planting specimen trees in large holes, and suchlike, trying to work topsoil into the rock where possible. Help please!

[Alisdair]

I'd be inclined to leave things as they are as much as you possibly can. If you are determined to plant specimen trees, then your suggestion of giving them a "comfort cushion" by mixing in topsoil in the planting hole may be necessary.
In our garden in Greece we did import topsoil into one new terrace, and have had more or less continual problems in that terrace! On the other hand elsewhere the (disturbed/mucked around but otherwise native) rocky stony ground has proved much more receptive.

[Vaughan]

Many thanks Alisdair, would be interested to know more about the problems you mention with the Terrace where you imported topsoil. I imagine the main problems come with heavy rains?

[Alisdair]

Mainly unexplained deaths! We were inclined to suspect something noxious in the imported topsoil, but now think it is probably just unsatisfactory drainage, in heavy rain, as you suggest.

[Alice]

Vaughan, we have imported topsoil on a number of occasions, as we also had very little depth of soil in most parts of the garden - measured in mms rather than cms. The quality has varied but generally has been good. We have had no problems apart from a great proliferation of very healthy weeds. Whether this was because the soil was disturbed or full of weed seeds, I don't know.
By the way, what would be the purpose of a membrane between the topsoil and the rocks beneath?

[Vaughan]

Ok thanks Alice. The landscape gardener we spoke to suggested a membrane for the shallow slope between the house and pool would need this to stop the topsoil being washed into the underlying rock and/or washed down the slope. However if the topsoil did get washed into the underlying rock, maybe this would be a good thing and would help retain pockets of moisture for roots to find. But I'm now thinking it might be better to terrace this area with stone walls, so that the beds would be flat.
Many thanks for your comments, great to get some experienced advice.

[Alice]

Vaughan, we have a gently sloping garden, so the plants and mulch largely prevent loss of soil after a downpour. In your case - a steep slope - terraces sound like a good idea.