I can easily spot rose-of-Sharon or shrub althea (Hibiscus syriacus) at this time of year, even when traveling at 55 mph. This deciduous shrub flowers during the torrid months of July, August, and early September.
Felder Rushing eloquently affirmed the toughness and durability of this old-fashioned shrub in his 2003 book, Tough Plants for Southern Gardens: “A drunk driver once ran over my great-grandmother’s old althea, and it came right back with new flowering growth. That’s one tough shrub if it can be pruned with a pickup truck!”
Depending on the cultivar, rose-of-Sharon flowers can be single, semi-double, or double in a range of colors that include white, pink, purple, lavender, blue, and red. In some cultivars, the flowers give rise to highly fertile seed pods, which can become a nuisance. I still remember a roadside rose-of-Sharon that I rescued more than a decade ago. I never realized that this single shrub would thank me with bazillions of offspring.
Fortunately, there are sterile to semi-sterile cultivars that have been selected for their compact nature (older cultivars are prone to legginess), gorgeous flowers, and few fertile seeds. Single-flowered U.S. National Arboretum introductions that produce few seeds include the pure white-flowered ‘Diana’, ‘Helene’ with white flowers and a red-eye spot, ‘Aphrodite’ with deep pink flowers and a dark red eyespot, and lavender-flowered ‘Minerva’.
Cultivars with semi-double flowers include ‘Notwoodthree’ (PP 20,574 Blue Chiffon® ) with blue flowers and the lavender-flowered ‘Notwoodone’ (Lavender Chiffon™).
Double-flowered cultivars, such as ‘Blushing Bride’ with double pink and ‘Lucy’ with double red-pink flowers, lack stamens or have few of them because their pollen-producing structures were converted to petals, called petaloids. However, they may retain normal functioning pistils (female fertile) whose nectaries attract pollinators, which can result in the production of some seeds.
Other double-flowered rose-of-Sharon cultivars, such as Peppermint Smoothie™ (‘DS04PS’ PP26551) with bi-colored red and pink flowers and Blueberry Smoothie™ (‘DS01BS’ PP26662) with bluish-purple flowers, are completely sterile. These cultivars have no male or female structures: their stamens and pistils have become petaloids.
While rose-of-Sharon will thrive in part shade, full sun results in the best floral display. Expect a mature height of 8 to 10 ft. high with a spread of 4 to 6 ft. Since rose-of-Sharon flowers are produced on the current season’s branches, prune them anytime in late winter, preferably with bypass pruners or loppers—not your pickup.