Hibiscus is a popular genus of flowering plants used in home gardening and landscaping. Hibiscus shrubs and trees are often featured as background plants or in groupings to take advantage of the showy large blooms they produce. Because of the feeding habits of hibiscus trees, application of fertilizer on a good schedule is recommended to maintain the health of the plants.
Hibiscus is a genus of plant that has over 200 species. Some are perennials and annuals, and most are shrubs. Some develop into small trees, but usually only when trained. The most common hibiscus tree is the Chinese hibiscus or Hibiscus rosa-sinensis, followed by the Rose-of-Sharon or Hibiscus syriacus. The tree appearance is the result of years of diligent pruning and shaping. Typical height of hibiscus shrubs and trees is about 8 feet.
The Chinese hibiscus is considered a tropical plant and, as such, does not overwinter well outside of USDA hardiness zone 9. These plants should be grown in containers and moved indoors before the cold temperatures arrive. They prefer lots of light and will go through a slowing down period once inside. Rose-of Sharon can overwinter outdoors in zones 5 through 9.
Type of Fertilizer to Use
Hibiscus is a voracious feeder, requiring regular feeding, especially if grown in containers. A balanced fertilizer of 10-10-10, 15-15-15 or 20-20-20 is recommended for all types of hibiscus. Micronutrients are also essential for the development of healthy hibiscus trees. Manganese and iron can be lacking in alkaline soils. Manganese sulfate can be helpful when applied 1 to 2 oz. per small plant or 1/2 to 1 lb. for a mature plant at each feeding. Iron deficiencies in alkaline soil may be augmented through the use of iron chelates such as Sequestrene 138.
When to Fertilize Hibiscus
Hibiscus requires frequent feeding, especially if grown in containers. Blended fertilizers should be mixed at half the label-recommended strength. For plants outdoors in the summer, give a dose every 2 to 3 weeks. For hibiscus plants indoors, fertilize once each month during the spring and summer and less frequently during the winter. Spring and summer feedings should be given 1) early in spring before budding begins, 2) after first growth appears, 3) midsummer and 4) late fall to early winter.
While hibiscus needs frequent feedings, it is important to remember that these feedings must be light ones. Overfertilization can result in damage to the hibiscus tree. Signs of overfertilization might include buds dropping before opening or the yellowing and dropping of leaves. If you have used a “bloom special” type of fertilizer with a concentration of 10-40-10, the hibiscus could be suffering from a buildup of phosphorous in the soil. High nitrogen content fertilizers can cause leaf growth but stunt blooms. Use care when selecting and applying fertilizer.