I planted a hibiscus in a container and now the leaves are turning yellow and dropping off. What do I do?
If you are growing a tropical hibiscus in a container, your plant may have severe transplant shock. Tropical hibiscus needs very loose, well-draining potting soil, often referred to as jungle potting soil. This potting soil dries out quickly so watering requirements are higher than with typical potting soil. The pot must have a drainage hole. If your plant went from an indoor location to outdoor sun, it is going to suffer. Keep it in the shade for a week or so then give it protection from hot afternoon sun after that. Repot it to correct drainage and soil if necessary. Give it bright but indirect sun and lightly fertilize. It is likely to recover. More info here: https://www.gardeningknowhow.com/ornamental/flowers/hibiscus/hibiscus-container-care.htm
Since you have just transplanted this hibiscus, the dropping leaves are probably caused by transplant shock. This is common with newly transplanted plants. Here's how you can help:
Here are some other ways to prevent yellowing leaves in hibiscus: