The hibiscus is a member of the mallow family, which consists of 250-300 species. These species include large shrubs, trees, perennials or annuals. Hibiscus has dark green leaves and is deciduous, meaning the flowers will fall off within a day. The plants can grow to 15 feet tall in frost-free areas. Flowers may be up to 6 inches in diameter with a wide variety of colors. In the northern climates, the most common species is the Hibiscus rosinensis. These are bred specifically for flower size and color but are not winter hardy.
Occasionally the leaves on a hibiscus will turn yellow. Several reasons exist for why this can occur and it does not necessarily mean that the plant is dying.
Water is important with this type of plant. The leaves can yellow from either too much water or not enough water. Check the soil daily and make sure it is moist. The leaves will turn yellow if the soil is too wet and soggy. They will also yellow if the soil gets too dry. If it is hot or windy, water frequently as necessary. If the plant is dormant, water it just enough to keep it from drying out completely.
Hibiscuses are tropical plants that are used to consistent temperatures that range between 65-85 degrees Fahrenheit. When temperatures in the summer become extremely hot hibiscus require additional watering. Otherwise the plant will dry out and suffer from heat stress. This can result in yellowing of the leaves. On the other hand, when temperatures get too cold, the leaves will also yellow.
Keep the plant away from drafts or windy places. This plant needs to be brought inside in places where there is winter. Transition the plant before you bring it indoors and before you return it outdoors in the spring.
Light is another critical factor. Too much sunlight can cause the leaves to yellow or even develop white spots that indicate plant burn. Remove the damaged leaves and move the plant to a different location. On the other hand, if the hibiscus is not getting enough light, the leaves may yellow as well. Again, move the plant to a better location.
Yellow leaves are also an indication that the plant is ready to go dormant. Bring the plant indoors and allow it to die down by reducing water. Once the plant is dormant keep it in a cool dark place for a couple months. Then cut it back and put it in a sunny window. Resume watering. When it shows new growth, begin fertilizing it again.
Sometimes, the leaf not only turns yellow but develops markings on the underside. This is the result of pests, such as spider mites. Spray the plant with soapy water or a pesticide. But do not overuse pesticides; follow the directions on the package--as overuse may, ironically, cause yellow leaves too.