The giant rose mallow has the largest flowers of any hardy perennial. Some of the hybrids may be one foot in diameter. Rich, moist soil and full sun bring the most vigorous growth, but mallows are very accommodating, and will tolerate light shade and less desirable soils. Giant rose mallows will flower from seed the first year if started very early in spring. Favorite cultivars may be rooted from cuttings during the growing season. Colors range from crimson, white, pink, rose, and in-between.
Giant rose mallows are relatives of the native hibiscus found in Louisiana and other Gulf South states. They are among the most spectacular and easily grown plants for use in the border. Following the spring and summer growing season, the plants freeze back to the ground each fall. Old stems should be cut back to a height several inches above the ground. New shoots emerge by mid-spring, and the plants quickly develop handsome mounds of foliage and flowers by early summer. Individual flowers last only a day, but each plant may flaunt several flowers at once. Numerous seedling selections, such as Southern Belle' and 'Frisbee' are offered in good seed catalogs. Few garden plants provide so much enjoyment for so little care.
Seeds of giant rose mallows are available from catalogs, while container-grown plants are usually in stock at Texas garden centers and nurseries. Color selection is possible when you purchase blooming-size plants. If growing giant rose mallows from seed, it is important to start them early in the season so that they will have adequate time to develop before freezing weather sets in.
Hibiscus mutabilis is an old-fashioned perennial or shrub hibiscus better known as the Confederate rose. It tends to be shrubby or treelike in Zones 9 and 10, though it behaves more like a perennial further north. Flowers are double and are 4 to 6 inches in diameter; they open white or pink, and change to deep red by evening. The 'Rubra' variety has red flowers. Bloom season usually lasts from summer through fall. Propagation by cuttings root easiest in early spring, but cuttings can be taken at almost any time. When it does not freeze, the Confederate rose can reach heights of 12 to 15 feet with a woody trunk; however, a multi-trunk bush 6 to 8 feet tall is more typical. Once a very common plant throughout the South, Confederate rose is an interesting and attractive plant that grows in full sun or partial shade, and prefers rich, well-drained soil.
Hibiscus coccineus is better known as the Texas Star Hibiscus. It has large, single, red flowers about 3 to 4 inches in diameter that appear atop branches of palmately lobed leaves with three to seven segments. Culture is very easy, with well-drained soil, an annual application of fertilizer in spring or early summer, and a sunny location being most important. Texas Star Hibiscus may be propagated from seed or cuttings. Mulching the plants in wintertime prevents root injury during very cold weather. Old stems, if they freeze, should be pruned back to the ground in early spring. Even if frost damage has not occurred, it is still a good idea to prune back and shape the plants before growth begins.
Consider hardy types of hibiscus for the back of flower borders where their impressive flowers can appear over other summer flowering plants. Some gardeners and landscape professionals plant daylilies, lantana, gomphrena, zinnias, portulaca, purslane, celosias or other summer annuals and perennials in front of their hardy hibiscus groupings.
Several years ago, Dr. Jerry Parsons, Extension Horticulturist located in San Antonio, released a new giant rose mallow named 'Moy Grande' from the San Antonio Botanical Garden. 'Moy Grande' has huge flowers of dark rosy pink. Best availability is in the San Antonio area.