Just bumping this up. I want to know about when they go dormant in 9a.

Don't have one, but now I think I want one!

Here's what I found when I looked it up:

"The Texas Star hibiscus (Hibiscus coccineus) grows in U.S. Department of Agriculture plant hardiness zones 5 through 10, although it may die back to the ground each fall in zones 5 through 8. Hibiscus shrubs can reach up to 8 feet tall in areas where they don't experience winter dieback, but in colder regions or with pruning, they grow to only about 4 feet high...."

https://homeguides.sfgate.com/care-star-hibiscus-32714.html

Perhaps the one going dormant now is in a slightly different microclimate - maybe getting a bit less light?

Some hardy type hibiscus do seem to go dormant early here. Others don't get going good till fall. I'm hoping mine will flower a little more before fall sets in. Grasshoppers have been horrid this summer. They have been devouring all the hibiscus leaves so bad they barely flowered plus they ate up the seed pods.

Thanks Carol and SJN. Yes, it was getting very little sun, and I think it was TOO wet (if that's possible, because they love wet spots). My other one up on the hill doesn't get enough sun either, but it isn't dying back, so all I can think of is it was kept too wet. Neither have bloomed, so I definitely have to find a sunnier spot this year. My fall-blooming hibiscus (H. acetosella, H. radiatus) are doing great and I can't wait for them to bloom.

Funny that it says they only go dormant in z8. That must be old info before they changed the zones, because my friend has one in Z9b (he sent me the seeds) and his goes dormant as well. Even when I was in Z10a, my perennial hibiscus went dormant in the winter, and some didn't come back if we had a freeze, but the Texas Star always did. I had it in z7a in SC, and it came back every year and bloomed like mad all summer long.