Hi Cozy, bought two Bobos last yr both in full bloom...this yr one is in full bloom the other has just 4 blooms...full bloom gets all day sun the other 4/5 hrs of sun....not worried young plants.. they were 3gal. Pots

I have a Little Lime that did that on its third year, 2nd winter. I am not worried unless it does it again.

Make sure you are not overfertilizing and watch for deer, bunnies, squirrels, etc

I put in seven Bobo's last fall that I bought off eBay for something like $5 each in tiny 2½" pots. Tiny. They are now just about the size of that in OP's photo or a tad smaller.

Most of them are blooming right now and those that are not are getting ready to. I am in a similar zone, so I think there may be hope for yours yet- nursery grown plants often come with screwed up schedules for the first season or so.

Thanks everyone for your insights and encouragement.

hyed, what is this beautiful cobalt blue hydrangea M. That you have?

Oh, so it is Mathilda that has an amazing blue! It is gorgeous! Your soil must be acidic. I would love to have blossoms with such deep color!