Growing trees in containers can be a challenge but fun. I like to grow trees in containers where it is not possible to plant them in the ground. Trees that normally remain small seem to work best. Early spring is a good time to prune if you are comfortable doing it. The green container for the Stewartia may be a problem if you want to repot the plant because it is smaller at the top than the bottom. It looks like the buds are beginning to swell and I would not do anything to it now unless it was absolutely necessary. I often leave trees in the same pot until they split the pots and then repot in a container that is about the same size by pruning the roots and top. I water with dilute fertilizer to give them nutrients when they are growing. The pine should be able to stay in the whiskey barrel as long as you want. Evergreens seem happy in pots for me. I have lost them from cold winters occasionally.
