Hardy hibiscus is not a single species, but refers to a group of hibiscus plant species and cultivars that exhibit frost tolerance unlike their close relative, the tropical hibiscus. Grow hardy hibiscus and enjoy the large showy blooms from summer to fall.
Hibiscus plants are deciduous, upright, bushy shrubs of medium texture. Hardy hibiscus shrubs generally range in height from 3 to 15 feet, with a spread of 3 to 12 feet. Their large, open flowers are striking in appearance and bloom in shades of white, pink, purple or red.
Plant hardy hibiscus shrubs in rows to make a large hedge, or use it as a specimen plant or accent in the landscape. According to a University of Florida Extension fact sheet, some species may be used in marshy areas, and species such as swamp rosemallow (Hibiscus grandiflorus) can be used in coastal areas due to its salt tolerance.
Grow hibiscus species in full sun or very light shade, in nutrient-rich, well-drained soils (depending on the species--some tolerate wetter conditions than others). Some species, such as H. moscheutos, require more chilling hours than others to produce the best new growth, so they are better suited to climates colder than USDA zone 9. Other hardy hibiscus types are hardy in zones 5 through 12, depending on the species. Propagate hardy hibiscus by softwood cuttings or by seed.
Rose of Sharon, also known as althaea (Hibiscus syriacus) flowers from summer to fall, with white, pink or purple blooms with red bases. It grows to about 10 feet tall, with a 6-foot spread, and is hardy in zones 5 through 10.
Hibiscus moscheutos has white, pink or red flowers and blooms from summer to early fall. H. moscheutos grows 3 to 8 feet tall, with a 3-foot spread. It is best for zones 5 through 9.
Hibiscus mutabilis flowers are whitish-pink to deep pink. The plant grows 6 to 15 feet tall with a spread of 5 to 12 feet. This species is less frost-tolerant, and is suitable for zones 8 through 12.
Pests of hibiscus include nematodes, aphids, mites, whiteflies, mealy bugs and grasshoppers, but the most serious pest is larva of the hibiscus sawfly (Atomacera decepta). The primary diseases affecting hibiscus include fungal leaf spots. Your local county extension office is a valuable source of information regarding pest and disease identification and management.