Hi, welcome to g o y, firstly, 12-15" is not very wide for growing anything, could you widen the borders to about 2-3ft, which would give you a far wider choice of plants or shrubs, also we would need to know the conditions, eg which direction does your garden face, how much sun does it get, sheltered or exposed, clay, sandy, or a nice loam, alkali or acid, all these factors have a bearing on what can be grown, sorry to answer your question with more questions, but it does help us to help you, Derek.