1092 Hibiscus grandiflorusCommon Names: giant rose mallow, swamp hibiscus, velvet mallow,giant hibiscus Family: Malvaceae (mallow Family)
Giant rose mallow is a big herbaceous perennial, sometimes reaching 10 ft (3 m) or more in height, and often developing a semiwoody stem near its base. The palmately three-lobed leaves are grayish green and velvety fuzzy top and bottom. They are big too: up to 10 in (25 cm) long and across. Hibiscus grandiflorus - the name says it - has grand flowers, with five six-inch (15 cm) petals which are pale pinkish violet with crimson bases. The spectacular flowers open in the late afternoon and are finished by noon the following day, but a succession of blooms (up to a dozen or more per plant each day) keeps up the show from mid summer through autumn. A happy giant rose mallow plant grows bigger each year by adding additional stalks from its root crown. We've seen plants with a dozen stalks arising from a root crown 2-3 ft (60-90 cm) across. White flowered specimens have been reported, as have hybrids with scarlet hibiscus (H. coccinea), which often shares a wetland with giant rose mallow.
Hibiscus grandiflorus occurs in fresh and brackish marshes and the edges of swamps, ponds, streams and ditches on the southeastern U.S. Coastal Plain from southern Louisiana to Florida and coastal Georgia. It often finds itself standing in shallow water.
CultureLight: Provide full sun. Moisture: Giant rose mallow grows in wetlands. It is not drought tolerant, but once established, giant rose mallow thrives in ordinary garden situations that get at least an inch (2.5 cm) of irrigation per week. Hardiness: USDA Zones 7 - 10. Giant rose mallow dies to the ground (or should we say "mud"?) in winter, but regains 10 ft (3 m) or more of height in a single growing season. Propagation: Collect seeds when ripe by removing them from the dried pods. Scrape a seed with a file to break through the hard exterior seed coat and expose a small area of inner seed, or use a needle to poke a single hole into the seed. Seeds so treated and planted in damp medium will germinate in a few days. Plants started from seed should begin blooming in their second year. Giant rose mallow also is easy to propagate by dividing the root mass.
Hibiscus grandiflorus has one of the largest flowers of any plant in North America, rivaling even the spectacular blossoms of Ashe magnolia (Magnolia macrophylla subsp. ashei). If you have a wet area, a pond or stream margin in full sun, or an area that gets watered frequently, you need one or more of these grand beauties. They are welcome in my vegetable garden (along with halberdleaf marshmallow (H. laevis) and scarlet hibiscus (H. coccinea), where I make sure they get an inch (2.5 cm) or more of water each week. In the afternoon hours before fully opening, the flower bud reminds us of a big tube of pink lipstick.
We love to grow the native American Hibiscus, and this one is our favorite. It's the largest North American Hibiscus and has the largest flowers. It's the only one that is fragrant, and the only one that blooms at night. Giant rose mallows commonly grow in large stands in freshwater and brackish marshes, and a mass in full bloom in the moon light is breath taking! All aiming their huge ultraviolet faces to the heavens, I have always supposed they were trying to attract some kind of gigantic extraterrestrial moths. (No doubt from the "Butterfly Cluster" in the Constellation Scorpius.)
Steve Christman 8/23/08