Hibiscus is one of the most versatile perennials with flowers blooming from spring until fall. A member of the mallow family, the hibiscus is related to cotton and okra, and can thrive in hot conditions. Flower colours range from white to orange, with pink, red, yellow and apricot often seen. Depending on the type of hibiscus and cultivar, flower sizes range from 2 inches to 12 inches wide.
Hibiscus plants enjoy full sun to partial shade. The type of hibiscus being cared for determines the watering needs and soil drainage requirements of the plant. The tropical or Chinese hibiscus (Hibiscus rosa-sinensis) needs well drained soil. Hardy hibiscus can be planted in wetter soil, "a great way to plant marshy areas that are otherwise maintenance problems," according to an article from the University of Florida extension service. On the farthest extreme of harsh water conditions is the swamp rose mallow (H. grandiflorus). It is salt tolerant up to and including brackish water in tidal zones.
Hibiscus plants like a lot of organic matter and soil nutrients. In addition to these requirements, the Texas A&M extension service recommends "small monthly applications of a complete fertiliser" from April to September to encourage continuous blooms for plants grown outdoors. For tropical hibiscus grown in pots indoors, the North Dakota extension service suggests using a houseplant fertiliser that is high in phosphorus and potassium and lower in nitrogen. Nitrogen encourages shoot and leaf growth, and the hibiscus is a prolific grower even without a high nitrogen fertiliser. For any fertiliser regimen, fertilise only during a time of active growth.
As a horticulturist with the North Dakota State University Extension Service wrote in an article about hibiscus, "Hibiscus plants thrive on being pruned, so pruning will not hurt them. In fact, pruning will increase flower production." In much of the south, tropical hibiscus can be pruned back one third to one half in early February to keep a bushy appearance. Many perennial hibiscus die back to the ground in colder climates. Clear out the dead wood. The Rose-of-Sharon (H. syriacus) blooms on new growth, with pruning done before new growth appears. Like many hibiscus, it can be pruned to shrub height or grow to the size of a small tree.
The tropical hibiscus is not winter hardy. Flowers last one day, but there are hundreds of cultivars because it makes an excellent container specimen. The perennial marsh mallow grows large white flowers. It is found in swampy areas, while the Texas Star (H. coccineus) and its red flowers takes drier conditions and grows 6 to 8 feet tall. Another perennial, the Confederate Rose (H. mutabilis) can grow 15 feet in one season and blooms in the fall. Rose-of-Sharon is a deciduous shrub that blooms from summer until the first frost, in good or marginal soil.
The large number of plants in the hibiscus family present a vast number of choices for indoor or outdoor cultivation. The key difference between hibiscus plants is whether the plant is a tropical hibiscus or hardy perennial. If it is tropical, it has to be brought indoors to overwinter, and it does not like wet feet. If it is a hardy perennial, it can be planted in most U.S. yards, and should tolerate wetter conditions than most other perennials.
- University of Florida IFAS Extension: Hardy Hibiscus for Florida Landscapes
- North Dakota State University Extension: Questions on Hibiscus
- Texas Cooperative Extension: A San Antonio Favorite, the Chinese Hibiscus
- University of Arkansas Cooperative Extension Service: Hibiscus
- University of Illinois Extension: Chinese (Tropical) Hibiscus