I have many of these planted in blasting sun in a reclaimed gravel yard. They are 2 years old and are coming into big blooms.
Only thing I can think of is that your plants last year had those long release fertilizer pellets from the nursery and the bloom buds were already formed(?) They use alot of pelleted fertilizer around here. This year your shrubs are trying to root themselves(?)
I put lots of compost and some organic shrub fertilizer around the plants this spring. I guess I am saying this because you describe the leaves and blooms as small.
Your plants get sun? I think the 'anabelles' like some sun.

Thanks for the reply, Franeli! You might be right about them just working on their roots this season. I planted them with composted cow manure and then mulched around them. They're on the west side of my house and get about 3 to 4 hours of direct sun, but not enough to wilt them. I think I'm going to ask the nursery about their tiny blooms and see if they confirm what you said.

Pruning is a major factor in developing huge flower head with AnnaBelle hydrangeas. Cut to several nodes above ground level for huge flowers in spring. Also the flower heads start out small and the get larger so you could just be looking at a developmental phase.

I have one also that was sold as Annabelle but has small blooms. I saw somewhere that they can revert to the native arborescens which i assumed was what had happened to mine. :(

I will definitely prune more aggressively next spring, but I'm also wondering if what Logan33 said was what might be happening... my plant looks suspiciously like the wild version of the Annabelles. I don't think the blooms are in a developmental stage since the florets are opening now, and even the florets themselves are teeny tiny.

I have a Hydrangea that has about one hundred small Annablle like flowers. It was a free cutting with out a name. A causal observer may call it an Annablle, but it only flowers on old wood. The flowers are about 2 inches across.

Gary

mine is a nikko, but this may apply. i have two shrubs planted at the same time and were the same size. both planted int eh front border. one, placed in original ground of mostly clay. the other, placed in an area we had to fill in due to a new sidewald raising the ground level. we filled this in with a load of topsoil @ 6-10". this one receives more sun to the point of wilting but is still techincally filtered shade. it is almost 3 feet tall. the other in the original clay in full shade to filtered is 1' tall and the blooms are a quarter the size of the one in replaced soil. i say in my circumstance, it is the soil making the difference b/c the roots penetrate better. funny, since they are less than 30 yards apart you wouldn't think there would be much diff.