Plant taxonomy classifies rose of Sharon, also called "althaea" or "althea," as Hibiscus syriacus. Contrary to its common name, the plant is not really a rose at all, belonging, instead, to the Malvaceae or "mallow" family. Nor is it thought to be native to Syria, in spite of its species name, hailing, rather, from the continent of Asia.
Characteristics of the Plant
Generally speaking, rose of Sharon bushes can get 8-10 feet tall, but their width is only about half that (they typically have a spread of just 4-6 feet). Their shape and relatively substantial height invites comparison with other tall, tree-like shrubs. However, some cultivars stay shorter (for example, Hibiscus syriacus 'Minerva' reaches only 5-8 feet). Blooms on these shrubs can be white, red, lavender or light blue; some have double blooms. Most bear small, deeply-lobed, light-green leaves (this trait may vary according to cultivar).
Although naturally a multi-stemmed shrub, this plant can be trained through pruning to have simply one main trunk; thus some people refer to it as the rose of Sharon "tree." Prune in late winter or early spring, since this is one of the shrubs that bloom on the current season's growth. It is easiest to give rose of Sharon its desired shape by pruning it accordingly during its first two seasons.
It can also be trained for espalier.
Zones, Sun and Soil Requirements for Rose of Sharon, Pest and Disease Problems
The climate is most favorable for growing rose of Sharon bushes in USDA plant hardiness zones 5-9.
Rose of Sharon prefers full sun and well-drained soil. Older bushes may fall prey to fungal damage if you are growing them in areas without full sun.
That is because excess moisture is retained in shaded areas, and it is precisely in moist conditions that fungus thrives. This plant does profit from growing in a rich soil, so fertilizing is recommended (although not mandatory for established shrubs). If you wish to stay organic, work compost gently into the soil around the root zone and water it into the earth.
The chief pest problem for this bush is Japanese beetle infestations. Happily, Japanese beetles are somewhat easier to control than many other insect pests, because they are large enough to spot immediately -- before they have done too much damage to your plants. The easiest and safest way to kill them is to pick and/or shake them off by hand, dropping them into a container filled with soapy water. The insect breathes through its skin, so a coating of soap over its body effectively suffocates it.
Uses for Rose of Sharon in Landscape Design
Three popular uses for this bush are as a:
- Hedge plant
- Foundation shrub
It's attractive and plentiful blooms make this plant fully capable of holding its own as a specimen. One's ability to shape rose of Sharon also makes the shrub a prime candidate for hedges. But since this bush is deciduous, it makes an effective privacy hedge only in summer (select one of the evergreen shrubs to gain privacy all year).
Still, it could be used to achieve privacy around swimming pools in regions with cold winters, since you would most likely be doing your swimming there only during the summertime. However, be aware that its blooms could attract bees, which are usually unwelcome visitors in poolside areas. Because the shrub responds well to an annual pruning, it is quite useful in foundation plantings, where it is important to be able to manage a plant's growth (to avoid having it eventually overwhelm your house).
Outstanding Qualities, More Growing Tips
Rose of Sharon blooms profusely, and its attractive flowers are its main selling point. Like other types of hibiscus, its flowers bear a striking stamen. Another feature giving the shrub value is its relatively late period of blooming (in the Northeastern United States, it blooms in August).
Rose of Sharon is thus able to offer color when many flowering shrubs have long since ceased blooming. It is critical for gardeners to be able to grow such late summer flowering shrubs if they are intent on managing sequence of bloom in their landscapes.
A heat-lover, this shrub is also prized by growers in the Southeastern U.S. who crave plants that can stand up to summer's heat. The plant is reasonably drought-tolerant. In fact, if your rose of Sharon has yellow leaves, it could be due to over-watering, rather than to a lack of water.
Do not give up on rose of Sharon, thinking it is dead just because it has not leafed out by early summer. This plant not only blooms late but leafs out late, as well, so be patient. When an althea's flower buds are not opening, that is another matter.
Nor are those the only problems associated with growing Hibiscus syriacus. Its seed drops and sprouts where you do not want it to, and the consequent need to remove the young plants manually is hardly conducive to low-maintenance landscaping. For those seeking help in this matter, I do, however, offer an alternative to pulling up the unwanted volunteer plants in my article on getting rid of althea seedlings.
Rose of Sharon is not the only type of Hibiscus that flourishes outside of tropical and sub-tropical regions, although when you hear that genus referred to you may very well think immediately of the tender types seen on display in greenhouses. Another hardy hibiscus is Hibiscus moscheutos, known for its giant-sized flowers.