That cultivar would not be my first choice for a containerized hydrangea. It just wants to grow too large and unless you consistently up-pot or root prune, you risk the shrub becoming rootbound rapidly and with somewhat stunted growth.

This cultivar is recognized as having the largest panicles/flowerheads of all the paniculatas. To encourage larger (but fewer) flowerheads, in late winter or early spring thin to 7-10 of the strongest primary shoots. But be aware the weight of the very large panicles may bend down the stems.

Gardengal, what cultivar would you recommend for a dramatic potted plant? I live in a city where I have no dirt.

Paniculatas tend to get large so, in pots,, I would use very compact paniculata cultivars like Bobo, Strawberry Sundae or Fire Light Tidbit. Check their dimensions before buying. Maybe use a half wine barrel as a pot for medium or large paniculatas. Or you could use other types of plants (by themselves or combined with other plants) if those paniculatas are not "dramatic enough". Or let the container be the dramatic one.

Thanks, luis. I’ve been doing this a long time. I do use large pots. I also have a Bobo and a mop Bridal Gown. I have a 12-yr-old honeysuckle, climbing rose, dwarf crape myrtle, bamboo, azalea and several smaller perennials.

Could fertilizer have been an issue?

"Could fertilizer have been an issue?"

Unlikely. But it depends on what you used and the frequency. What is most likely to affect growth and appearance will be the planting medium, the size of the container vs. the rootball and the time since the last repotting and any root pruning.