I have two trees in planters in my backyard in Brooklyn, NY - a Stewartia Pseudocamellia, and a Japanese Umbrella Pine. I'd prefer that they not grow to full size - it's a small yard. But of course, they've grown, raising questions.
Should I get larger planters?
Should I prune branches and/or roots?
Should I do both?
Is this a good time for pruning or transplanting into larger planters? It's March 3rd, and through the weekend it's going to be between the 20's and the higher 30's.

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.

Trees grown in containers actually have the potential to live longer than their counterparts in the landscape. This is because where trees naturally occur, they are predisposed to mechanical injury, which is what starts most 'wild' trees circling the drain.
The key to good health is regular root work, which includes removal of all or most of the soil, root pruning with a focus on removing large roots not growing horizontally and not attached to the base of the tree, and regular replacement of the grow medium.
The tree below was also being air layered off of it's old roots, and the layer was separated during the repotting. You can see the tourniquet wire. The tree (Japanese maple) was from seed and seedlings typically have roots too unsightly for bonsai w/o a major overhaul.




Questions or additional input?
Al