Convert concrete area to flower bed

Hi all,

I am attempting to convert a concerted area into a flower bed which will mainly host some small shrubs.

I have removed the paving slabs and underneath is a dry mix which I am digging up now. The problem is that it is very wet and soggy underneath as before this was grass and someone has just put the dry mix and concrete slabs on top of the grass.

My questions is, how deep do I need to dig down and then what do I fill the hole with to ensure drainage?

If it helps my location is North West England, United Kingdom and the weather tends to be cool and wet

Thank you in advance.

 

bump

 

What I would do is take off the dry mix and then dig it over, I'm unsure how deep, maybe a foot, then you will have a better idea of your soil and if it stays wet or drains well, which in turn will help you decide what you need to do or not to do, hope this helps a little bit.

 

Is the soil is constantly wet I would go for plants that enjoy those conditions.