"Would September be a good time to move this Annabelle and perhaps divide it ?" Yes, the earlier in the month the better in zone 4. Then water in well and mulch well to help keep the soil evenly moist and insulated so it stays warmer longer for good root growth. Mine do great in morning only sun.

I have been doing some hydrangea divisions and they have been remarkably successful. Dig up the plant and wash off the soil. Washing off all the soil will give you a chance to inspect the roots. Look at the root ball and see where the plant can be divided into two or three pieces with roots attached. Wiggle them apart - you might have to cut the sections from the top of the ball but try to select sections with lots of roots. Cut broken roots and check for insects or shoots that look mushy or just not solid and cut those off. Be as gentle as possible - take your time pulling the sections apart. If you split some of the larger branches growing out of the root - don't worry they will be ok and probably root just fine when planted under the soil line. Put them in a bucket of water to re-hydrate and then plant in new -- ordinary potting soil - not organic - in a container with drainage holes. Professional growers have found that organic potting soil is too rich for new and divided plants and can top kill the plant. Do not put rocks or anything over the drainage holes! Not needed and NOT recommended. Soak the soil and let drain. Put the new plants in the shade - or speckled shade - just not direct sun for a couple of months. You could reduce the height by 1/3 if you want a shorter plant but be sure to cut just above a leaf node. Do not fertilize. Keep the plans moist but not soggy. I would protect the new plant for the first winter - garage or car port. You plants should do just fine in their new home.

Thank you so much to the both of you! I will be moving and dividing it tomorrow following all your advice...

In all honesty, with Annabelle, you can just whack a chunk off the side, and I don't imagine it will need winter protection its first winter as long as it's planted soon and well mulched. It is a suckering plant, so sends out side shoots that then put down roots. I've divided my Annabelles numerous times by just digging up some of the side shoots and putting two or three in a pot, plastic bag, or box together with some dirt and watered them in well. I usually trim off most of the leaves since they have reduced roots and are no longer attached to the mother plant. They've grown well, no problem. The older the part of the plant, the more difficult it will be to dig up.

Thank you so much La la la. Love to see the difference. I'm pretty sure now, that what I moved is Annabelle. Although if wild hydrangea's blooms also start green to turn white then green again before drying up like paper... you could be right.

Is that the case?

Also, when I transplanted it, I found a long piece of dead mother root almost as fat at my wrist! All other major stems had rooted from it years ago...

We'll see for sure next Summer which of which. Only if I've done my transplant/division right.

Annabelle makes that set of color transitions.

Thanks, then for sure is it...