Answer: It's normal for the oldest leaves of your hibiscus to turn yellow and fall off. New leaves will be produced in their places. If both the new and the old leaves of your plant are turning yellow, it could indicate a need for nutrients or that the soil isn't draining quickly enough to suit it. I'd feed the plant and water deeply once or twice a week (depending upon weather). As temperatures cool down, your plant should grow and flower well for you.
Best wishes with your garden!
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