I have several seedlings of Betula albosinensis and Betula utilis, and
I would like to try growing some of them as multi-stemmed trees. I
understand that this can be achieved by pruning them to the ground,
after which multiple stems are thrown up. Could anybody help, please,
with the following questions?

1) At what stage in the tree's development should it be done, e.g.
how old, or at what thickness of stem?

2) When would be the best time of year to do it? I know birches can
bleed a lot of sap.

3) Does this method of growth have an impact on the tree's mature
height, i.e. will I end up with a shorter tree?


Thanks very much in advance.