They may live out in the water more-so in zone 9 vs zone 5. We get long frozen periods, maybe that is why. I am sure the species are more hardy they usually are. I did grow a hibiscus in a pond and it did great for me, but pulled out and heeled into dirt/mulch for the winter.
When it was in the pond, it had no soil, just bare roots in water. Used a rock to weigh it down so it wouldn't float around.
