Hi, do you know which pecies of Hibiscus you have ?, there are about 200 to choose from, ranging from frost tender to fully hardy, so it's impossible to give you a definitive answer, without knowing which species you have, having said that, the most likely species to be sold in the U K is H sinosyriacus, or H syriacus, the former growing to about 8ft high, spread 10 ft, the latter 10ft high x 6ft, but all Hibiscus need a long, hot summer to flower well, and if your weather has been anything like ours, they won't flower well, and it could just be caused by cold, damp conditions, they also like a humous rich, moist but well drined, neutral to slightly alkaline soil, and full sun, Derek.