"Don’t think you can plant trees in containers? Think again. These birch trees are placed in large containers, and because the root ball is kept from growing outward, the whole tree remains smaller and more manageable."
Hydrangea paniculata 'Limelight', large white blooms tinged with pale green; trailing Ivy at the base spills over the sides of the classy zinc planter boxes. Baltic Ivy (variegated creamy edge) would combine well too.