I want to create a bed in front of a retaining wall (west facing). There is room for 30 cm soil before concrete foundation underneath. Can that be enough to plant shrubs such as Choisya/Berberis/Pittosporum if soil prepared properly? I want to avoid a raised bed and container planting if possible.
It is too shallow for trees or tall shrubs that will not have enough anchorage and it might need watering during the dry months, so a simple drip irrigation system might be set up at planting time.