The leaves on my Double Red Althea are turning yellow and falling off. I have not been overwatering it. I did not water for several days until its leaves were starting to droop. I then watered sparingly. Any ideas? Thanks.
How long has the plant been in the ground? Hibiscus, especially newly planted one, tend to overreact to drying out too much and Rose-of-Sharon (H. syriacus) is no different. Most likely it got a little too dry and the rocks-as-mulch amplified the effect by heating them up and cooking the roots a little. The leaves that are currently yellow will probably still fall off but it shouldn't get any worse.