Topsoil - How deep?

gasbill

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.

nodwah

I definately replied to this y'day but it didn't go on for some reason.

Anyway i saw on the telly someone said that grass roots are only really shallow like 2 inches maybe so that wouldn't need to be deep.

As for the border, that could be as deep as you can afford

When i dug over some ground last year, that had been under slabs, it was very compacted and anaerobic - really smelly, so I thought it best to turn it over a bit and break it up and let the rain etc at it for a few weeks to aereate it. I covered it with HM compost and shrubs and flowers are growing fine now.