hello all. we have a vertical rockery/retaining wall outside our kitchen window and about 1 meter away from it. this is about 1.5 metres high, then a small plateau then it rises again for another 1.5 meters.what plants would be suitable to grow in the soil between the rocks to give us some colour to look at instead of bare rocks and the weeds that grow there? something that will take hold quickly if possible to brighten the area up. thanks in advance for any advice.