There is no need to worry about keeping the rootball intact if you are container growing, but for a really rounded pot you might have to break it to get the tree out.

In any case, once the tree is as big as you care for it to be, you will cease up-potting and start root pruning. Every two to three years you pull the tree from the pot before bud break. Then you cut off the bottom third of the root ball with a saw, and make pie shaped slices out of the side. Shake of whatever else soil you can and re-pot in fresh soil.

After you've done this a few times with no negative results you will stop treating root balls gingerly (beware....in mid summer this rough treatment can be fatal).

JustTrees

Thanks for the advice.
I had no idea that rootballs could take that kind of treatment.
Once a maple has been root pruned and re potted does it require any sort of special care ? Would you expect normal Spring growth to take place ?

Spring will be like normal, although the tree growth will slow down as the root mass becomes limited. This is why large trees that grow 30' tall in the landscape will limit out to perhaps 15' tall in a pot.

If you don't root prune the tree will die. The whole container will fill with woody roots and there will be no root hairs to pick up water. When pruning your are getting rid off woody anchor roots so that new feeder roots can grow.