Macs probably start within a 2-4 week range of each other. At different times every year. Most serratas probably start, as a group, before macs. It's all a function of genetics, weather, etc. too many factores...

Thx. I guess the time lapse I had in my mind is not going to grow exactly as timed...just feels kinda off. It's like the young ones are saying we got energy to produce and bloom so move over big bertha.

What do you mean by "new"? Just planted this season? Newly planted bigleaf hydrangeas will often bloom before those already established in the garden as they were grown by wholesalers located elsewhere and often provided additional heat, light, fertilization and growth hormones unavailable to those plants already in the garden. They are unlikely to bloom as early or as heavily the next season :-)

New as planted, acquired in 2017. Let Dance in Dirt.

ES and Bloomstruck in pot.

One ES and Bloomstruck overwinter outdoors in the elements all winter. One ES overwintered in a friends cold frame as I wanted to compare.

So just short of the the one ES that was in a cold frame, all above saw winter elements. I did ~baby~ them by walking into the 24+ inches and shoveled the tops out and created a ring to keep the snow off the Let's Dance...So maybe they are paying me back in spades with blooms ?

I do the dig out on alot of my shrubs though.....I hate finding splayed surprises. Lost too many in the past due to such.

BTW, GG, I'm aware nurseries use growth retarders to maintain shelf space, and or maintain/delay grown for mothers day blooms. etc. Growth hormones ;-)

You got my eyes perked. How many I make small shrubs into your 5 ft mature plants before I see my kids grow up and move out. I don't think I can wait 7 years +

IME in addition to the effects of even sometimes small cultural differences and how established they are, different cultivars may have differing bloom times.