I have received several calls and messages from home gardeners and professionals about Hibiscus with yellow leaves. This is normal and usual for Hibiscus anytime the weather shifts. Changes in weather, temperature, and water make Hibiscus leaves yellow.
Hibiscus plants are favorites in warm landscapes worldwide. Across South Florida, they are plants not well adapted to local soils. They prefer soils with an acidic pH. However, soils with an alkaline pH are found throughout South Florida. High-pH soils tie up the iron and other trace elements Hibiscus needs to grow healthy green leaves. Iron deficiencies are common in Hibiscus, which is characterized by yellow leaves.
Hibiscus requires regular fertilization to maintain healthy and vigorous growth. Hibiscus blooms and grows best when fertilized three or four times per year. Use a balanced fertilizer with trace elements for the best growth. The trace elements can help reduce some yellow leaves caused by nutritional problems.
Also, this temperamental shrub prefers partial shade or some shade from the hot afternoon sun. Bright light is a good thing; too much heat is not. Deep shade is not appropriate; it leads to poor growth and blooming. Either condition produces yellow leaves.
However, Hibiscus can produce yellow leaves with little provocation. Some causes include over-irrigation, under-irrigation, too much rain, alkaline soils, planted too deep, changes in the amount of water, changes in the temperature, such as when a weather front sweeps through the area, windy conditions, old age, and pest problems. Hibiscus that have been in the ground for 7+ years have high root nematode populations that reduce plant vigor and result in the frequent production of yellow leaves.
Yellow leaves are common with Hibiscus. An abundance of rain, cold temperatures, and shortening days are all causes of the recent spate of yellow leaves on Hibiscus. If soil issues, problems with planting location, and maintenance of the plants have been eliminated as the cause, then the yellow leaves on Hibiscus are due to the weather conditions. If it is just a few, pick the leaves off and go on about your business. Do not prune or fertilize the plants. If more than a few leaves occur, look for other problems, such as one of the common causes listed above, correct any associated problem and watch for growth as the weather warms.
This column and image first appeared in the Treasure Coast Newspapers.