Hi, I have 2 hibiscus that I over wintered in my house. They both have several leaves on them that are dull and leathery feeling. They are still green, they are just a very dull almost dried out looking green. I've searched the web looking for what it could be but haven't found anything like it. They weren't fed all winter and most of last summer. Now that I know they need to be fed year round unless they go dormant, I have started feeding them with a special blend hibiscus food from hidden valley hibiscus. Anyone have any idea what this could be? Also, there are no bugs.