PlantLife Online

Answer

Yellow leaves are not a death sentence, the plant is just trying to tell you something. You will need to do some investigation, possible causes could be too much water, not enough water, too much light, not enough light, too hot or cold. In your case since it is the bottom leaves I would guess it is not enough sun light or a watering issue. Hibiscus syriacus prefer moist well-drained soil and a hot sunny location. If the plant continues to decline it could be a soil borne pathogeny like a virus or verticillium wilt. Hope this helps, let us know how it goes by posting a comment on your question.