Answer: A hydrangea tree is usually a PeeGee hydrangea (Hydrangea paniculata, a woody shrub) pruned or trained into a small tree. This type of hydrangea would have white flowers and does not change color.
Kousa dogwood (Cornus kousa) blooms in late spring to early summer, well after the native dogwoods (Cornus florida) have already bloomed. It should not need much pruning if any at all. It is better not to prune it if at all possible as pruning opens the bark and can serve as an entry to pests or diseases. If you should need to prune it, for example to tidy a branch that has become broken during a winter storm or to remove a badly rubbing branch, I would do that in late winter on a day when temperatures are above 40 degrees.
Enjoy your new trees!
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