[Tahi]

I seem to remember being told not to prune my sumach tree or it would sucker
profusely. It gets surrounded by other growth all summer and has grown very
lopsided with all the growing branches at one side, at least six feet away
from its trunk. There is no sign of any suckers. How hard can I cut it back,
and can I do it now, while I can see the problem!
I am in North Wales and my first daffodil is out today.