Posted: 29/09/2013 at 09:46
Just saw this thread- agree with Verdun- not the right spot for things like Heucheras and AStrantias as they like a bit more shade. If you want all year round structure, ie some evergreens, Hebes will do well there. If you combine them with a contrasting shape like Phormium you'll get something very effective and you can add some softer spires of a perennial of your choice in between to give contrast. The slope means you can plant things of the same height and it will give a nice appearance as you'll see all the plants as you drive in. I wouldn't worry about the wall being different heights.
As to drainage, it doesn't always follow that the top will be better drained than the bottom- mountains are just as wet at the top as they are at the foot! Water will run down the slope there, but as long as the soil is well drained where you plant into it, it won't really make a difference. Clay soil will hold water where plants are put in regardless of a slope, so if the soil is sticky clay you might want to get a bit of grit dug in there before you plant, especially when it's all been recently constructed. The ground probably needs a bit of oomph put back into it.
Did that make sense? I know what I mean!