That is strange - they are blooming like gangbusters here all over the place without anybody doing anything for them. We call them 'Rose of Sharon'. The pure white ones are so beautiful. Do you fertilize them? Do you have them in pots? Can you post a picture so I can get a sense of what's going on? Fertilizer sometimes does more harm than good. They don't need it. Shade or Sun? They need full sun: >6hrs/day. These shrubs are a hands off kind of deal. They don't want fussing over. All I do is prune a little here and there.

They are late to come into leaf anyway. They are often in flower when you buy them because they are root-bound in containers. When planted out they tend to put on lots of leaf at the expense of flowers. I would feed only potassium (sulphate of potash) and nothing else for this year and see if that makes a difference.

I have three hibiscus in my allotment garden, these were dug up from a French garden, they were self set seedlings about two ft tall, they did not flower for about three to four years but now flower every year and have many flower buds on at moment, agree with Bathgate I never feed them at all they are in a south facing situation, so maybe be patient and given time they should flower, I will be putting on a blog for the allotment garden and will include some pics of hibiscus, in the near future.

Thank you for all your advice. I have tried to send a photo but I cannot seem to find any where to do, so I will try all your advice and see how it goes. Thanks again.