"Peter"
:

I have a little - 2' 6" approx - oak tree in a 18" pot. How long can I keep
it?

Depends how good you are at looking after hardy native bonsai trees. If you
can get it through the first 15 years it should be ok for the next 150.

If you move it down into a shallower tray shaped pot it may need some
shelter during especially cold winters, it's no good letting the whole
rootball freeze, and it may need watering every day in very hot dry summers.

Root pruning every other year and some leaf pruning when the buds first open
in spring will keep it in shape.

Andy R
--
http://www.europa.usenet.eu.org

Europa.* is the usenet hierarchy for europe wide
topics without language restrictions.