I live in Seattle. My condo board is having a debate about
whether pruning an ornamental cherry after May will kill it or
not. Can you help? Also, when should it be pruned?
According to Cass Turnbull of the local organization, Plant Amnesty, the
main reason pruning ornamental cherries is problematic is that the branch
system of these trees is complex, and it is hard to tell (if you are not
an experienced gardener or a professional arborist) what to prune. In her
Guide to Pruning (Sasquatch, 2006), Turnbull says that ornamental
cherries are prone to dieback if their branches are shortened. Besides
the dieback issue, improper pruning can give rise to watersprouts (the
branches grow straight up). I consulted two other pruning guides, both of
which advised against any pruning of ornamental cherries.
Do you know why the board wants to prune these trees? If the trees are
too large for the site, it might make more sense to remove them and plant
something appropriate which will not require risky pruning. You may find
this discussion forum from University of British Columbia Botanical Garden helpful.
Excerpt:
“These generally disease susceptible trees resent severe heading back.
Trying to force it to become a perfectly symmetrical shape will also
destroy its natural character; much of the appeal of aged Japanese
cherries (and related trees) is the contrast between the prettiness of
the flowers and the rugged appearance of the trunk and branches.”
My summary is that, while pruning the trees may not kill them outright,
it could make them aesthetically unappealing and more susceptible to
disease, so it would be best to let them be.