I have bad news for you. In a zone 6b, there is an extremely good chance you can kiss your Endless Summers goodbye.

You can grow the Hydrangea species paniculata, arborescens and quercifolia. Plenty to choose from. Hydrangea macrophylla is not one of them.

You can certainly grow Endless Summer hydrangeas in your zone!! And a fair number of other new wood flowering macs. However, there is a very good chance they will die back to the root crown each year unless you offer some sort of winter protection. If subject to that annual dieback, they will never achieve their mature size. I wouldn't expect to see them grow much beyond 3' (I have seen them get 8-10 feet tall and as wide in my very hydrangea suited climate).

I've had Endless Summer for about 8 years at least and it has a couple of blooms once in awhile. Most of the time, it dies back to the base and it's supposed to bloom on new wood, but...I'm in z6b and I'm replacing mine.

I know I have posted pictures of a neighbour's Endless Summer hydrangeas before. They do beautifully and she not 'a gardener' and doesn't do anything special for them. They are in a raised bed on the SE side of her house. They look like this by early July and stay like that for a long time:

This is what they looked like on May 20 this year as the foliage was emerging both from the base and at the lower end of the stems (you can see that she prunes them down in the fall, which you aren't supposed to do.... She also doesn't give them any winter protection.):

So I'm not sure what she is doing 'right' but she grows them well here in Zone 5(b)!

Great thank you,I have them growing and they're green and growing they had a rough time time last year,they were new,blooming then in last summertime had problems. This year they've grown and very green no buds but getting small ones I just want to know how tall they could get 3-4ft or more like