I have a very large potted Hibiscus. Over the past few months, it has thinned considerably. The leaves were yellowing and now have developed brownish blacking spots underneath the leaves. Any help you can give me would be great.
Certified GKH Gardening Expert
Lack of enough light and pest problems are two possibilities. Check for any small insects or mites on the leaves. Also check for fine spider web-like material, which is a sign of spider mites. See this article: