Topsoil - How deep?

gasbill

I know this is a bit of a gardeney one, but thought I'd try here.....
I have just had a large slab of concrete removed from my garden, but there is a hole with a lot of hardcore in it left, which I will cover in topsoil. I'm wondering how deep it needs to be? I don't want to put topsoil down, and discover that nothing will grow as it's not deep enough, with all the hardcore underneath it. I will be planting some of it with lawn, and some with herbaceaous perennial border. I guess the lawn part doesn't need to be as deep as the border. The man who removed the concrete said it didn't need to be too deep, but if anyone has any advice, it would be gratefully received.
Thank you in advance.

gingerbits

I would say a lot depends on whether this patch is likely to dry out easily - if it is in full sun I think you'll find it difficult to grow perennials well with less than 12" topsoil - but if it is a shady, moistish spot you'll get away with 9" if you don't choose very vigorous or shrubby type plants

BUBBLES_3

I would recommend that you try to remove the hardcore or the area may drain too quickly and become very dry. If you cant then see if you can put a layer of thick turf (grass side down) on top before you put down the soil. I would say you would need at least a spades depth of soil and keep digging in the garden compost.

gasbill

Thank you - guess I'll have to start digging and shovelling - it's a dry, south-west facing slope, so I expect drainage will be a problem...will try and get rid of as much as possible.