Hi - I'm a first time gardener, (my only experience to date is a few pots of gerianiums outside my front-door.) I'm trying to create a flower bed around the perimeter of my lawn but yesterday I discovered a layer of concrete in the flower bed area about 5-6 inches down!!!! - so now I'm a bit worried that this area will not be deep enough for a flower bed. I want to have a mixed border with mainly evergreen shrubs, 3-4 azealas /camelias, maybe a hydrangea but also room to plant spring/ autumn bulbs and summer /autumn perennials so that they come up in between the permenant shrubs and plants.
Because of the concrete, I'm now thinking I may have to resort to building a raised bed, so I'm trying to work out how deep this will need to be. I've read that rhodendrons have shallow root systems and that they don't go too deep (so I'm assuming azealeas don't either) but I can't find anything to tell me what will be 'deep' enough to accomodate the root systems of the plants I want to grow. Would another 7" be enough to make the entire depth up to 12 inches?
If I do have to create a raised bed then I'll do it with wood or sleepers as I've used sleepers elsewhere in the garden and don't want to have too many different materials in the garden but then again I don't want to use too many sleepers and make it too high as I don't want the structure to be too dominant as the garden is small and I need to make a L shaped border. So I suppose my question is do you think I would get anyway with just one sleeper height above the ground so that the entire depth is then raised to 12 inches ?