Care for plants in pots -
Anything you plant in a pot will eventually become pot-bound so it's worth preparing for that reality. It will also struggle for moisture and nutrition unless you help it out, Every Spring, scrape off quite a lot of the compost and replace with new compost (it's called 'top-dressing') which does mitigate the plant struggling for nutrients. I add horticultural grit as a surface dressing as it holds the moisture well in Summer.
You're basically putting the plant in a 'cage' and preventing its roots from reaching down into the earth to gain nutrition so you need to give it access to some nutrients and water. I say that reservedly because you don't want to feed it excessively, as it will put on a growth spurt and become pot bound even sooner. The top-dressing helps to revive the plant in the Spring.
I commented on another thread that hydrangeas don't like being in a pot long term (hence why your's is struggling).
Hebe look good in a pot as their growing habit is quite compact with pretty blooms, but OMG once they become pot-bound, you will have problems getting it out - they can even crack a terracotta pot, their roots are so solid!
Roses can look nice, especially the ones grown specifically for pots, David Austin have several varieties worth looking at on their website.