[Lardman]

North facing wall - 5ft high 20ft long. Soil is very thin (2inches maybe) sandy and full of stones, sub soil is red sand / gravel (good enough to lay brick with ). The area was damp but should be very free draining now I've dug it over, it was infested with bindweed / creeping buttercup so I expect regular weeding will be required.

I currently have 2 blackberry bushes planted at 5ft spacing being trained on wires this leaves me with 3 x 5ft gaps to fill. max depth 8" otherwise whatever it is will get stomped on by my clumsy feet.

[Mahogony]

I'm also interested in the answers to this question, I've a bit of wall that sounds similar.

[gillie]

Trained gooseberry bushes?

Gillie

[Lardman]

Trained gooseberry bushes?

Im all soft fruited out and I've never been a big gosgog fan. Ill keep looking, it seems such a shame not to make use of the space.

[Yorkie]

Whatever you grow, you'll need to consider how you will retain fertility in the soil.  It's a very shallow top soil layer, and the subsoil as you state will be very free-draining, meaning that nutrients will dissolve away rapidly.

Can you enrich the soil with LOTS of organic matter (manure, compost, leaf mould, etc) before starting, and then mulch deeply with it too?

That's before you start considering what may survive in such conditions.