Does anyone have experience with hibiscus? Last year I was given 4 hibiscus: one white, two red (all in the same pot). I put two of the red ones in a different pot and gave them to a friend. I kept the white one and one red one, and they've been together in one pot since then.

The plants seemed to be doing great, and they'd been continuously putting out buds, until about 2 weeks ago. The white one is fine and even has 2 buds that will open soon, but the red one...In the last couple weeks more than half of its leaves turned yellow and fell off. Only about the top third of it looks normal.

The plant is by a East facing window (slight southern exposure too). I water it when it seems dry, about twice a week. Those conditions have remained constant. Am I doing something wrong?

The really weird thing is that today I talked to the friend to whom I gave the other two red ones. She's having the same problem. Is it some kind of dormant period? It just seems like a lot of leaves to lose at once. And what about the white one? Will it eventually do the same thing?

Thanks for any help you can offer...