Summer Pruning of Weeping Cherry (Prunus subhirtella x 'Snow Mountain')

Weeping cherries should be pruned before the weather starts to cool. Here, in the Northwest Hills of Connecticut, this means no pruning should be done after Labor Day. Cherries need the time to 'harden off'. Pruning too late in the Season will result in branches with new growth that will die back because they do not have enough nutrients or sugars to be sustained.
The tree in this video is Prunus subhirtella x 'Snow Mountain' but the techniques for pruning it apply to all cultivars of Prunus subhirtella.
Bop shows the proper techniques for pruning this particular type of tree.

[@amywilkins1402]

So is it ok to trim in the summer? I was told early spring or late fall. It is touching the ground and driving me crazy!