Hardy Hibiscus

If you like gaudy, showy, outrageously flashy flowers then hardy hibiscus is the plant you want to grow. Rose Mallow, as it is often called, is native to the wetlands of the American southeast, which gives the plant another common name, Swamp Mallow.

The huge, saucer shaped blooms have a tropical flare, but don’t confuse them with the tropical hibiscus; these are hardy to at least zone 5. Most gardeners will find hardy hibiscus easy to grow and a glorious finale of late summer color in the garden. 

Hardy Hibiscus plants are superb for marshy, wet areas, poolside and rain garden plantings. Smaller varieties make impressive container plants.  The flowers are attractive to bees, butterflies and hummingbirds also.

Hibiscus moscheutos, the hardy hibiscus, is often confused with Rose of Sharon, or with tropical hibiscus. They are often all mixed together in garden shops. Rose of Sharon is also hardy, but the plants have woody stems, which survive the winter, and the blooms are smaller. Tropical hibiscus has large flowers but the leaves are different, smaller and lobed, and the flowers are often shades of yellow, and orange or doubled. The leaves of hardy hibiscus are broadly triangular in most varieties, and the flowers of hardy hibiscus do not come in true yellow and orange and are generally single.  

There is an Asian species of hibiscus, Hibiscus mutabilis, hardy to about zone 7, that does have double flowers and leaves shaped like maple leaves. It is sometimes called Confederate Rose Mallow. The Confederate Rose Mallow has broad, lobed leaves somewhat like a maple. To add to the confusion this species has been crossbred with H. moscheutos, producing interesting varieties for gardeners, but still more confusion in the garden shop. Hybrids may have purple leaves that are 3 lobed, somewhat like a Japanese maple leaf. If you are looking for true hardy hibiscus, check the plant label for zone hardiness and a Latin name.

The flowers of hardy hibiscus are round and flat, ranging from 6 inches to more than a foot across. They are shiny, with prominent veins radiating out from the center and a sort of crepe paper look. Hardy hibiscus has enlarged stamens and pistils in the center of the flower, often in a ring of contrasting color.  Colors of hardy hibiscus range from white through shades of pink and red, including a plum red that is almost purple. While there is one variety that claims to be yellow, it is a very pale cream color at best.  Many flowers have a ring of darker color in the center. Each flower is open only a day, but mature plants with plenty of moisture produce enough flowers to make a long show, usually blooming from late summer to frost.

Growing Hardy Hibiscus

Hardy hibiscus or Rose Mallow can be started from seeds and if started early indoors, may bloom the first year. The seeds are slow to germinate and need to be kept constantly warm and moist. Start them at least 2 months before your last frost and transplant outside after all danger of frost has passed.  Hardy hibiscus is also sold as a potted plant, or as dormant root pieces. Potted hibiscus should be planted in the ground soon after you buy them, at least six weeks before your first fall frost, for best survival of the first winter.

Hibiscus prefers full sun and moist soil. They will grow and even bloom in part shade, although the plants won’t be as full and flowering stems may need staking. Some varieties will require staking even in full sun, especially in windy areas. Hardy hibiscus plants produce several stems from the ground that may reach 5 foot tall or greater in moist, sunny areas.

Rose Mallow isn’t fussy about soil, but that soil should be kept well watered; the plants will thrive in rain gardens or marshy areas. A slow release fertilizer can be used in the spring as shoots emerge.

Hardy hibiscus dies to the ground in the winter. The location of the plants should be well marked as they are very slow to start growth again in the spring, waiting until the soil reaches about 70 degrees before sprouting new growth.  This late start is why zone 5 is about the limit for growing hardy hibiscus, they may survive zone 4 winters but not have time to bloom before frost.

Some named varieties

Disco Belle comes in white, pink and red flowers. The plants are compact at 2-3 foot with 9 inch flowers.  Southern Belle is larger, at 4-5 foot high, and has flowers 10-11 inches wide in a range of pink, red and white.  ‘Kopper King’ is one of the hybrids, it has purple foliage and huge, light pink flowers with a red eye and red veining. ‘ Crown Jewels’ also has the purple foliage but on a more compact 3-4 foot high plant, and white flowers with a red eye that are about 6 inches across. ‘Moy Grande’ is a huge hibiscus, plants may reach more than 5 foot tall and the rosy red flowers are over 12 inches across.  ‘Old Yella’ is the closet to yellow hibiscus, actually a creamy white, 10 inch flower on a 4 foot plant. ‘Plum Crazy’ has deep, plum-red, 10 inch flowers on a compact 3-4 foot plant with purple foliage.