I have been given a tall planter, about 80cm x50cm, it fits in well with my garden and I want to put something really impressive in it, either a single tree or shrub, or a thriler-filler-spiller combo. Site will either be a fairly dry south west facing terrace or in a cooler south part of the garden, and it won't be moving again because it weighs a tonne.
Any ideas or inspiration for something with deep roots that might grow well in a tall planter?