Out
On A Limb / August 2006
Rose of Another Name
The Rose of Sharon is a hibiscus rather than a rose. As members of the mallow family, they are related to hollyhocks, cotton and okra. Their scientific name “Hibiscus syriacus” comes from the Greek word for mallow and syriacus, for Syria, where it was once assumed they originated.
Traditionally cultivated for profuse blooms and appreciated for its causal maintenance requirements, Rose of Sharon has been losing admirers for immoderate propagation habits. In July, the US Department of Agriculture listed Rose of Sharon as a Weed of the Week for escaping intended plantings “to invade, crowd out and displace more desirable native plants.” The national flower of Korea, Rose of Sharon is reported invasive in Kentucky, Pennsylvania, Tennessee and Virginia. In some landscapes, this time honored favorite has become a nuisance.
Still, the large, colorful blossoms of the plant variously called althea rose, shrub althea, shrubby Althea or Syrian rose are very attractive to many gardeners–and hummingbirds. The flowers have little scent but they do produce nectar for hummingbirds and for the tiny insects that hummingbirds dine upon.
The blooms come in white, light blue, pink, mauve, lavender, purple, and red. Some have double blooms, others are bi colored and most bear small, deeply-lobed, light-green leaves, depending on the cultivar. Rose of Sharon leaves don’t come out until late in spring, but the woody shrub will bloom non-stop from July through September, usually closing its four inch petals at night.
The variety of cultivars is extensive. Hibiscus syriacus ‘Aphrodite’ has pink to mauve single flowers with a dark magenta eye. Hibiscus syriacus ‘Ardens’ is a mauve to purple double-flowering plant. The striking Hibiscus syriacus ‘Bluebird’ is blue to lavender with single flowers that have a dark magenta eye. Hibiscus syriacus ‘Red Heart’ has pure white single flowers with a scarlet eye. ‘Blue Bird’ has blue flowers and ‘Diana’ has white flowers that stay open all night.
Native to India and East Asia, Rose of Sharon was introduced as an ornamental and is often used for hedges as well as a single flowering specimen. It can be propagated from root cuttings but it reproduces primarily by seed and it is a prolific seeder with a deep taproot can be extremely difficult to remove once the plant is established. Since plants bloom on new growth, shaping or pruning can be done at any time. Most Mid-Ohio Valley gardeners prune them in late winter or early spring.
Rose of Sharon grows in full sun to light shade and prefers a well-drained, humus-rich, fertile soil but is very adaptable to various soils, poor soils and a range of soil pH from 3.7 to 7.3. Salt tolerant and drought tolerant, it can survive soil compaction, heavy pruning and pollution, making it one of the most urban-tolerant plants. Although the bushes generally can grow to ten feet and have a spread of four to six feet, special cultivars, like Hibiscus syriacus ‘Minerva’ can be just five feet tall. The many naturally occurring stems can be trained through pruning to have simply one main trunk, resulting in a Rose of Sharon ‘tree’. It’s best to give Rose of Sharon its desired shape by pruning it during its first two seasons when it is easily established. It can also be trained for espalier. Older plants that are never pruned tend to eventually arch and bloom less.
Since blooms occur on the current year’s growth, it’s best to prune in early spring before new growth starts.
One third of the wood, including the oldest branches and any weak growth at ground level, should be removed annually
Their long blooming period, plentiful, showy flowers, adaptability and low maintenance make Rose of Sharon a welcome addition to the garden as a specimen plant, at an entranceway, in a row, as a border shrub, or as a formal or informal hedge.
Beware older cultivars that set heavy seed crops. They can self-sow to form a weedy colony of young shrubs. Controlling the progeny of Rose of Sharon can be a task in an untended garden, but sterile cultivars for Rose of Sharon may solve their multiplication problem. ‘Diana’, ‘Helene’ and ‘Minerva’’ are now available at the U.S. National Arboretum. PL
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Femme Fair 2006
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