Hardy Hibiscus Care

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 flair, 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.

Hibiscus moscheutos 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 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. This species has been crossbred with H. moscheutos, producing interesting varieties for gardeners but still more confusion in the garden shop. 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 six 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. 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.

Hardy hibiscus plants produce several stems from the ground that may reach five feet tall or greater in moist, sunny areas. The leaves of H.moscheutos are broad triangles or heart-shaped and are dark green. Hybrids may have purple leaves that are three-lobed, somewhat like a Japanese maple leaf. The Confederate Rose Mallow has broad-lobed leaves somewhat like a maple.

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 two 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 partial 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. 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.

Choosing varieties

Disco Belle comes in white, pink and red flowers. The plants are compact at two to three feet with nine-inch flowers. Southern Belle is larger, at 4 to 5 feet high with 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 three- to four-foot-high plant with white flowers with a red eye that are about six inches across. Moy Grande is a huge hibiscus; plants may reach more than five feet tall, and the rosy-red flowers are more than 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- to 4-foot plant with purple foliage. Red Flyer is a very different hibiscus; a hybrid of two little-known American natives that grows up to 12 feet high, with narrow, lobed foliage. It has flower petals of scarlet that are narrow and don't overlap, and it is hardy to Zone 6.

The Confederate Rose Mallow, H. mutabilis, comes in single- and double-flowered varieties but is only hardy to about Zone 7 and begins blooming very late, around October. In the far South the stems may not die back in winter.

Using hardy hibiscus
Hardy Hibiscus is an excellent plant for late-summer color in beds and borders. They 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.