They prefer cooler, damper conditions than those that have prevailed down South this year - my surfinia petunias on my balcony have looked like they do at the end of October for the last 3 weeks, so even they've had trouble coping with the heat.

have you deadheaded regularly ,Isometimes find the ones in containers and baskets have to be fed reg. and watered daily otherwise tthey can look sad quick.Like Bamboo says they are not to happy in full sun that could be a reason.