How close are you planning to plant against the exterior wall. I would add 2 extra feet if you are planning for a tight shrubline against a perimeter wall

I only ask as I planted a speced size of 3x3, in which I gave it a extra foot of clearance, knowing that that there was a possibility I might end up having to dig and replant it further out.

Planted 3G last year. Speced as 3x3. It's not 2 feet high yet, but overall width, it's 2 feet. If it grows another 12 inches next year, I'm going to need to do some moving...

H. serrata Tuff Stuff has been a reliable bloomer for me for several years and is just about 3’x3’. It’s pH and Al dependent for bloom color and is a lace cap. It dies down to the ground every year and is still blooming by early summer.

I would second Bobo, Little Lime, Little Quickfire, Tuff Stuff and the new, albeit speculative, introductions from Proven Winners: Little Mauvette, Wee White and Limetta. But I would not recommend Bombshell as it is the only paniculata that a lot of owners posted that it was not blooming for them, at all, after multiple years of ownership in cold zones. It was kind of weird for such a winter hardy shrub actually.... I even contacted the wholesaler for comments and received an email saying do not prune it. Oh well. So much for getting answers... probably from a Q & A Sheet, hu? Hee hee hee. ;o)

After getting off to a slower than expected start (no flowering until second year but best after year 3), Bombshell has done exceptionally well for me!! Except when the deer beat me to spraying repellent on the flower buds :-)

I too had no luck with Bombshell...did not flower for me after a few years in ground.

Bobo is my favourite hydrangea...flowers buds are already forming on them...which is great as Bobo normally blooms much earlier compared to my other panicle hydrangeas.

What about Strawberry Sundaes? These are also compactish as well. I have a few planted a few years now and they are still under 3x3.

I just happened to return from one local nursery where they had stock from Garden Debut, a hydrangea wholesaler. They had a variety called Pearls N' Pink, which they say gets to 3' tall and 4' wide:

http://www.gardendebut.com/plant/Pearls-N-Pink-HydrangeaI did not mention SS because White Flower Farm and the Missouri Botanical Gardens rate SS as 4' tall.

It looks a lot like H. p. 'Dharuma' which is dwarf.