Ask Mr. Smarty Plants

There are 12 species of Hibiscus native to North America, of which 3 are known to grow in California. It doesn't really matter though, because you almost undoubtedly have one of the many hybrids, and/or imports from other countries. Both the hybridization and being non-native would put them out of our area of expertise, but we can ask you some questions which, when you answer them, could give you a clue to what's going on.

1. How many times has this hibiscus repeated this behavior of dropping leaves twice a year? If it was once, it may have been the result of some change in its environment. If it has happened multiple times, you need to look at where it is growing and how it is growing.

2. What sun does it get? Hibiscus can grow in a little shade, but they do best in full sun; that is, 6 to 8 hours of sun a day. 

3. Is the plant in question growing in the same area as the other 7? If not, what is different about where it is, as opposed to the others? Again, soil moisture, sun, even accidental exposure to a pesticide could have caused the leaf drop.

We found a website called "About Hibiscus", Hibiscus Care, that seems to have the most information on this plant. Read it and compare the conditions considered optimum for hibiscus with the conditions of the plant you are concerned about.