Seeding and area of lawn over an area of concrete?

[Corbygardener]

Hi people, hoping someone could help with this as I need to get it right first time! I have a circular area of concrete at the end of my current lawn area which I wish to turn into lawn aswell. The area is 6m by 6m and has a storm drain smack bang in the middle of it. I have tested the drainage of the bare concrete with the hose and generally the water ran straight to the drain. There were a couple of areas where a very shallow puddle gathered. I can comfortably get at least 10cm of topsoil on top of the concrete before I seed it but my main question really is will the concrete be better broken up? If I break it up, the water will drain through it but where to? Am I just better to leave it so the water will find its way to the drain? Apologies for all the questions within this post, but as you can probably tell, I'm CONFUSED!!

Cheers

Corbygardener[/img]

[rainbowgardener]

Well, I have raised beds sitting on a concrete patio and they do fine. But 10 cm = 3.9 inches right? That's not nearly enough soil for anything but the smallest most shallow rooted things. Not really enough soil even for grass.

Here's a quote:

Soil Depth

Grass roots are unable grow deeply in poor or shallow soil. Weeds thrive closer to the surface of soils than grass. If the soil in your lawn is less than four inches deep, grass roots cannot penetrate the deep ground to establish deep feeding roots. Four inches of soil is an absolute minimum for great growing organic grass. Eight inches (or even more) is preferred. Without deep soil, grass will dry out quickly and die off easily. When this happens, weeds have free reign over the area. Weed seeds germinate quickly and easily without the grass to compete for water and shade dropped seeds from the sun. As most weeds grow more towards the top of the soil anyway, it is of no consequence to them if they cannot send out deep roots.

Read more: http://www.doityourself.com/stry/organi ... z1Aj2tMKiq

If you have a way to put sides around your area and build it up a bit more, like 15 cm, your grass will do a lot better and you won't need to break up the concrete (which is a huge job, that's why my raised beds are sitting on concrete).

My raised beds are more like 50 cm tall, but that's because I grow tomatoes and all kinds of stuff in them...

[Corbygardener]

Thankyou for that. This morning, I have broken up a large amount of what I thought was concrete but turned out to be old tarmac mixture (about 3 inches thick, followed by extremley soft sandstone hardcore). Do you think now the material is broken up into small pieces and is about 4-5 inches thick, that a further 15cm of topsoil on top of that would work? I have read on other forums that all the hard material needs to be removed but I really can;t see that with the way it has broken up, with all that topsoil on top, that it would be a problem. If I did remove the hard core, I would need to get rid of about 8-10 tonnes of that and then invest in about 13-15 tonnes of soil!!!!!!!!!

Thankyou for reading

Corbygardener