How deep to replace dirt?
I have a gravel corner in my yard that I decided to plant. I started digging down to remove the gravel but I am down 18 inches and still all I see is more gravel! This is a strange house (converted carriage house)so I am thinking that gravel goes so deep for a reason. But I still want to put some perenniels there so my question is instead of digging down as far as I can go, just how deep does the dirt have to be in order to grow healthy perenniels?