Rose-of-Sharon is valued for large flowers produced in summer when few other shrubs bloom. It is useful as a garden accent due to its strict, upright habit. The open, loose branches and light green leaves make Rose-of-Sharon ideally suited to formal or informal plantings, and with a little pruning makes an attractive, small specimen tree. The plant grows in sun or partial shade and in any soil. Rose-of-Sharon grows 8 to 10 feet tall and spreads 4 to 10 feet. The growth rate ranges from slow to moderate, and transplanting is easy. Several roots are usually located just beneath the soil surface.
Scientific name: Hibiscus syriacus
Pronunciation: high-BISS-kuss seer-ee-AY-kuss
Common name(s): Rose-of-Sharon, Shrub-Althea
USDA hardiness zones: 5B through 9A (Fig. 2)
Origin: not native to North America
nvasive potential: invasive non-native
Uses: specimen; container or planter; trained as a standard; deck or patio
Availability: not native to North America
Height: 8 to 12 feet
Spread: 4 to 10 feet
Crown uniformity: symmetrical
Crown shape: upright/erect
Crown density: open
Growth rate: slow
Leaf arrangement: alternate (Fig. 3)
Leaf type: simple
Leaf margin: dentate
Leaf shape: rhomboid, ovate
Leaf venation: palmate, pinnate
Leaf type and persistence: deciduous
Leaf blade length: 2 to 4 inches
Leaf color: green
Fall color: no color change
Fall characteristic: not showy
Flower color: red, pink, white/cream/gray, purple, blue, lavender
Flower characteristics: very showy
Fruit shape: irregular
Fruit length: .5 to 1 inch
Fruit covering: dry or hard
Fruit color: brown
Fruit characteristics: does not attract wildlife; not showy; fruit/leaves not a litter problem
Trunk and Branches
Trunk/bark/branches: branches droop; not showy; typically multi-trunked; thorns
Pruning requirement: little required
Breakage: susceptible to breakage
Current year twig color: gray
Current year twig thickness: thin, medium
Wood specific gravity: unknown
Light requirement: full sun, partial sun or partial shade
Soil tolerances: sand; loam; clay; acidic; occasionally wet; well-drained
Drought tolerance: moderate
Aerosol salt tolerance: moderate
Roots: not a problem
Winter interest: no
Outstanding tree: no
Ozone sensitivity: unknown
Verticillium wilt susceptibility: resistant
Pest resistance: resistant to pests/diseases
Use and Management
The single or double flowers are in shades of red, pink, white and purple, depending on the cultivar. Individual flowers stay open for one day and close at night. Since plants bloom on new growth, shaping or pruning can be done at any time. However, pruning is usually not required since the plant grows slowly and keeps a tight upright form. Prune in late winter or early spring in northern climates. Frequent severe pruning gives fewer but larger flowers; no or little pruning gives many smaller flowers.
Although tolerant of poor soils and drought in sun or light shade, this upright, deciduous shrub requires ample moisture to flower its best and to avoid leaf-drop. Some protection from mid-day or afternoon sun is beneficial for optimum plant appearance. Tolerance to aerosol salt and wet soils combined with drought-tolerance make this a fine plant for many landscapes.
Many cultivars are listed but few will be seen in catalogs. Cultivars include: `Admiral Dewey' - single, white flowers; `Ardens' - purple, semi-double flowers; `Bluebird' - single, bluish purple flowers; `Boule de Feu' - double, purplish red flowers; `Coelestis', single violet blue with reddish purple throat; `Coerulis' - semi-double, light purple flowers; `Coerulis Plenus' - double, lavender flowers; `Diana', with pure white flowers, four to six inches in diameter, that stay open at night; `Duc de Brabant' - double, deep purplish pink flowers; `Hamabo' - single, pale pink flowers, with reddish stripes halfway up the petals; `Jeanne d'Arc' - double, white flowers; `Lady Stanley' - semi-double, white flowers with bluish pink on each petal and red lines running half way up the petal; `Leopoldii Plenus' - double flowers, blushed pink; `Lucy' - dark pink, double flowers; `Mauve Queen' - mauve flowers, `Paeoniflorus' - double pink flowers; `Red Heart', single pure white flowers with deep red center; `Rubus' - rose pink, single flowers, petals darker at the base; `Souvenir de Charles Breton' - semi-double, light purple flowers; `Totus Albus' - single, pure white flowers; `Woodbridge' - single flowers, reddish purple, darker at the base.
Propagation is by cuttings.
Although usually strong and easy to grow, hibiscus can be bothered by aphids which accumulate at the tips of stems, causing new growth to be misshapen. Aphids may cover the leaves with sticky honeydew. The insects can be dislodged with high pressure water sprays from the garden hose or controlled by pinching off the part of the twig with the insects. Over-fertilizing increases aphid infestations.
In northern gardens, Japanese beetles are particularly fond of the flowers.
If leaf spots are seen, pick off and destroy the infected leaves.
If bacterial leaf spot causes problems, pick off and destroy infected leaves.
Canker can kill branches or entire plants. Bright, reddish-orange fruiting bodies may appear on the bark. Prune out infected branches.
Flowers may be infected with a blight caused by a fungus.
Bud drop can be caused by too much or too little water or over fertilization.