Q.Hibiscus
Having bought three Hibiscus a few years ago – they were advertised as being white, pink and blue. They have been in large pots in the garden on a patio sheltered from strong winds but would get sun easily.
We had just one flower last year on the blue tree otherwise they have not bloomed at all.
Any reason you can think of as to why they do not bloom ? your advice appreciated

I think you may be talking about Hydrangea plants.
This article will help you.
https://www.gardeningknowhow.com/ornamental/shrubs/hydrangea/hydrangea-not-blooming.htm