I bought this Magnolia plant and put it in the front of my Cincinnati home
(zone-5?). The Kentucky Gardner that I purchased it from warned me that this
is about the lowest temperature that Magnolia can tolerate. Believe it or
not- it has survived 6 winters so far and doubled in size. How do I prune
the tree (it is not just a plant anymore)- so it looks more like a tree and
less like a big bush?