Yellow leaves are a sign of many things - too much water, cold weather, lack of fertilizer, spider mites or disease. Is it a hardy hibiscus in the ground or in a pot? What type of climate are you in? How long ago to you plant the hibiscus? Did you add plant food? Are other plants nearby turning yellow? I need a few more clues to solve the mystery of your yellow leaf hibiscus. Keep growing, Marianne Binetti