When is too late to leader-prune columnar arbs?
I have several degroot's spire trees that are still somewhat small (2-3 feet). Unfortunately, i couldn't find any with only a single leader, but i managed to at least pick some with a fairly dominant leader and a good columnar form.
I would like to make an attempt to gradually prune off any competing leaders, and I was wondering when (age wise) is too late to begin this? I understand that starting small (e.g., prune only parts of one leader at a time for gradual changes) is the way to go, but I can't find any definitive information on when starting this time of pruning becomes futile. anyone have any experience with this?