which variety of hydrangea is suitable for pots

Question

the pot is approx 50cms diameter and 36cms deep

Answer 1

While you don’t have to use dwarf hydrangeas in pots, you may want to if your space is limited. Hydrangeas don’t just get tall; they also get bushy. Look for plants specific to your growing zone and size constraints.

https://www.gardeningknowhow.com/ornamental/shrubs/hydrangea/hydrangea-container-care.htm