Petrocosmea grandiflora has been in cultivation since the late 1990's and was first introduced as P. duclouxii. It has a limited distribution in the wild, growing in cracks in rocky limestone cliffs in south-eastern Yunnan at around 2000m. Belying its tender appearance and provided that it is kept dry, it has regularly survived sub-zero temperatures under cold glass. Cultivation tips can be gained from the information supplied about its natural habitat - cracks in limestone cliffs - so a free draining compost that never becomes too wet is the order of the day. A 50/50 mix of loam,leaf mould versus gritty sand, perlite, fine bark based compost is a good starting mix.
Watering is the key to success and knowing when to do it will certainly improve survival rates. I use the 'Floppy test' - if the leaf feels flaccid to the touch, does not resist against bending then it needs moisture. If the leaf has turgor, feels firm when bent then watering should be resisted. Petrocosmeas in general prefer shady conditions and as such should be given adequate protection during the summer months. Flowering can be improved by exposure to low temperatures in the winter.