Hi, Quilter. I only have a few baby hydrangea's, so I can't comments specifically on them.
But, we did just move 3 juniper's, that were large with deep roots. I dug a much of the root ball as I could. For the couple of really stubborn deep deep roots, I did clip them. I filled the new hole with water, and planted them, and watered again, after I filled it with dirt.
The biggest thing I've found with any move, is to keep it well watered for a few days. I actually moved two of them in a drizzle, knowing it was going to rain for several days. They took extremely well. I think
spring is a really good time, as the
plant is just awakening, but not in full bloom, and the rainy season seems to help them in the move.