Even if you are not interested in "bonsai-ing" the trees, I think they might benefit from root pruning to stay happy in a container. If the root outgrows a container the tree might go into decline and eventually die. With regular root (and top) pruning, you can probably keep the trees alive indefinitely!

The pruning you suggest makes sense. I guess I DO need to check out some of the bonsai basics since that is sort of what I will have to do. Just guessing here, but do I take the tree out of the pot at some point and pare down and straigten out the mass of roots (thinking of the seven foot birch here), and also limit the height to which I let it grow? Should I put it back in the same pot then or go for a bigger one if I can find one? Is there a ratio of height that is appropriate to root mass?

Pruning container (or even in ground) trees is often done in Japanese gardens - its termed niwa-gi. I don't know much about it, but you could check on the internet or even ask on the Japanese gardens forum.

OH.. you can indeed grow them indefinately.. at a clients garden.. we had a willow planted in a container..never root pruned maybe 20 years... the root grew out the bottom of the container.. willows loving water so.. it grew down into the bricks on their roof and into the building.. one way is to keep getting larger containers.. also.. the top will dwarf it's self sometimes if the roots are bound.. Gordon

Try Linda Yang's book on city gardening. Everything you ever wanted to know about growing trees in containers is there. It's one of my bibles on balcony gardening.

Here is a link that might be useful: Amazon.com Linda Yang's book

Off to the library-- they have Linda Yang's book. Aren't libraries great? Thanks to all for your suggestions.