Hello, gle2011. Transplant shock will be less of an issue if you wait until the plant has gone dormant. So do this sometime in the Fall or Winter. But for Zone 5, I would divide/transplant well before your soil freezes. The next best time would be in the Spring. The worst time is probably when temperatures are hot. So, now is actually not a bad time to transplant either.

These are not strict rules, of course. For example, due to construction work years ago, I had to move some hydrangeas out of the way into a protected location while some roof work was being done. I then replanted them in the same spot. One plant broke into two by itself when replanting. This happened in mid-May, which is the start of Summer here and when we get into the 90s.

Many people have had success with division. Do a search in the forum if you want for keywords like split or divide. But... I always caution that hydrangeas were not designed to be divided so if, any of these plants has sentimental value, first propagate it via cuttings. Just in case... ;o)

Oh, and do not fertilize divided or transplanted plants until Spring. Just add 3-4" of mulch to protect the roots and to help keep the soil as evenly moist as possible. Helps with frost heaving too.

Luis

Now is a great time to transplant them in zone 5. Choose a damp day, and do it in the next week or so if possible. Mulch well and then keep an eye on moisture and don't let them dry out before hard freeze, but don't keep them soggy either. I wouldn't divide them since as Luis said they aren't usually of a growth pattern to split. If you have rooted branches you can clip them off and plant elsewhere, or next season weigh down a branch or two to encourage rooting.

Yes, typically woody-based plants - shrubs and trees - are not divided or split. However, caning shrubs - those that produce multiple stems from the root crown rather than just a single trunk - are somewhat more amenable to this practice just by growth habit. Often they will come apart or split on their own when transplanting but I would not force the issue. You can do serious damage to the mother plant if you attempt to divide and the plant is not similarly inclined :-)

Caning shrubs include most hydrangeas, shrub dogwoods, lilac, forsythia, beautybush and a lot of other early season or spring bloomers.

I wouldn't have guessed that ES qualified as caning since it my cold zone it doesn't really behave like my other caning shrubs.