Every year I buy a potted hibiscus with the hope that, at the worst, I won't kill it, and at the least, I can keep the leaves green.
Two years I actually brought a plant inside at the end of summer. One of those looked beautiful but close examination revealed dozens of spider mites, so I took it outside and left it exposed to the elements of a midwestern winter. Another year the plant, bursting with green foliage and blooms, gradually dropped leaf by leaf until only one healthy-looking sprig remained. Still, I was optimistic until my son, home from college, asked, "Mom, how's your stick doing?"
This year's plant sat on my front porch for about 24 hours before the first yellow leaf appeared. Hoping for a different outcome, I searched online tips and found a user friendly site: Hidden Valley Hibiscus, which listed these possible reasons for yellow leaves:
--Too Much Water (I did water it thoroughly when I brought it home because somewhere else I had read hibiscus like moist soil.)
--Not Enough Water (I stopped watering it altogether.)
--Too Hot (It's a tropical plant for crying out loud!)
--Too Cold ( I brought it inside a couple of evenings when the temperature dropped to an unseasonable level.)
--Too Much Direct Sunlight (I placed it on our covered porch, where it received about three hours of morning sun.)
--Too Little Sunlight (My mother, whose hibiscus sits in full sun and received five days worth of rain without having on yellow leaf -- suggested I move it, so I put it on the front porch step. There it did reward me with three beautiful blossoms before the yellow leaves returned!)
--Insects, Particularly Spider Mites (Oh really!)
--Too Windy (Remember the porch is covered; the plant unexposed)
--Improper Nutrition or pH (I repotted it using Miracle Grow potting soil.)
--Pesticide Over Use (Of course, I followed the manufacturer's directions!)
The article ends with a cheery note: "Good luck with your growing and gardening and by all means have fun with it!"