Putting a Disanthus cercidifolius in a planter.
I have a Disanthus cercidifolius I really want in a particular spot. The spot is nice, however, it pretty much has about an inch of topsoil and the rest is just clay, and I mean thick clay. I've read there a two options: building a mound or a planter box. The planter box looks the most sensible since the mound would have to be quite large to rise above ground level and the clay. My main concern, however, with planter boxes is mainly to do with drainage and its relation to the the size of the box since it will still have clay at the bottom. I guess my biggest fear is that the planter will be too small and in the long term the shrub will just become root bound in the planter itself. By that, I mean, where the planter soil hits the clay, won't it keep the roots that eventually make it down there waterlogged and unable to breach the clay? Is this a risk or do the roots generally not behave this way and stay near the top of the planter? So, generally, if the box is big enough drainage is not an issue?