Could be just a matter of immaturity. This is a very long-lived, very woody species. I have never seen an old specimen that had not flowered freely, often evidenced by the numerous large woody fruit that hang on for years.

G. thunbergia is not the same as G. volkensii, though they are rather similar. The latter is rare in NSW. It has more rigid, straighter branches and narrower leaves and is less ornamental, though more widely distributed in southern Africa.

Thanks Tony,
I had 3 Volkensii and about 8 Thunbergia, I just wondering because they looks similar.
How old should they be before they produce flower, I planted mine about 5 years ago, I got them from Flower Power and were severely prunned (I'm sure they were from cuttings) and now they grew to 1.5-1.8m, received full sun at least 6-8 hours a day.

I grew my Gardenia Thumbergia from seed 10 years ago. It is now three feet tall and healthy. It winters in a cool greenhouse 50% fahrenheit. I have never had a flower. Is there any possibility that it might flower, or is it very unlikely in the English climate? If not, I will have to dispose of it.