I took the advice of joanne and gardengal and cut three hydrangeas that were struggling from transplanting. I cut them from just over 5' to around 2' (where I could see healthy new shoots on many of the branches).

Should I also thin them out more? I don't know the variety, as they were rescued from a neighbor that had planted them in too small of an area and was going to throw them away. They were crowded in a 3' diameter half circle plot, along with a large camelia, so were very narrow from crowding.

Also, should I fertilize or just keep watered well; they were planted with lots of organic compost.

Here's one after cutting back:

And before cutting back, showing a few underwhelming blooms:

Thank you.