I know of some growing south of Sydney in Nowra but they were the plain white cultivar which appears to be more cold tolerant.

Andrew.

Yes I was surprised to read that they grew so far South as they are indeed a tropicial plant. So I think you are doing a great job if you are managing to keep them alive down there what can I say but just keep them warm and maybe some one from Sydney will answer your question.

Do you have the white one Mussaenda frondosa as Andrew said it is more tolerant to the cold, they like rich moist soil and a sunny spot. Good Luck with your plants

MM.

The true M. erythrophylla with single deep red 'bract' (actually a sepal) will grow OK in Sydney in a frost-free sheltered spot. The Botanic Gardens had it growing for years in their shrubberies. The plain white M. frondosa was once quite widely grown here and could be found even in suburbs that got a degree or two of frost. I haven't seen it around much lately

The 'philippica' types like Aurora and Queen Sirikit can survive in only the most sheltered sites in Sydney. I have never seen one that looked any good, but I guess with the right heat-trap spot you could get an attractive specimen. Even in the tropics they often look scraggy.

I am quite sure that mine are Queen Sirikit, I can really tell because the nursery did not know anything about them,
the reds did not survive the winter.
They quite nice in from sping to autumn, but dropped at least half of their leaves in winter, I'll post the pics soon.