Re the Cornelian Cherry (Cornus mas) I have grown C mas for many years and
have four trees in my yard. I do not feel that they are a single trunk
tree. All nurserymen that I have talked to say that it is a multi trunked
tree. I know some people that have tried to keep it pruned to one trunk and
it is a constant pruning job. Also as you prune out of season you have
wounds that can get infected. My point is not that you can't keep it pruned
to a single stem but it is more beautiful in most cases when you let it bush
out and has more flowers in early spring.
I call it my ChristMAS dogwood because of the C. mas and it blooms here
in late January or early Feb. It is a beautiful tree to be covered in
yellow blooms that time of the year when other things are not blooming.
Good luck in trying to make it a single trunk
Neb