This is normal for tropical hibiscus. In the winter they will get black spots and the yellow leaves are from too much water. They will be ok once spring comes. If you want to not have this happen again I suggest putting them in pots and bringing them in when winter comes. I live in So cal and I winter all my hibiscus.

Boy, I have never had this happen to this degree. I'm wondering if it is due to splashing up from the soil, and if I mulch more heavily with bark that might reduce the fungal contamination. I've got about 30 to 40 hibiscus planted in my yard, so there's NO way I'm going to pot that all up! I wouldn't begin to have that kind of room in my garage, either lol!! But, I think I'll mulch, and also try to innoculate everything with mycorrhizae. I've got about 1/2 of them already innoculated. That should help keep the bad fungus in check, if the mycorrhizae can populate, they'll compete for space with the bad stuff, and hopefully crowd it out next winter when we get our rains.

Patty S.