Iris,
I always let the root system dry out on buttonwood before I haul it out
of the pot to do a re-pot. There is less chance of damaging any roots.
If there are few roots,(at least where we are), it may take a year for
new roots to completely fill the pot under good growing conditions.
-A free draining mix with some organic, warm and humid, good light,
fertilize year round(the only time my buttonwood doesn't get fed is in
the fall when temperatures are lower before I bring it in.) If you don't
feed it well in winter the plant will slow down, the leaves will loose
their luster.
And unrestrained top growth will help build a root system that has been
damaged.

Now I have to trim some trees.

Best regards,
Alan

Blue Mountain Bonsai
Ontario, Canada
Zone 6