Rose of Sharon, (Hibiscus syriacus, or Althaea syriaca), shrub or small tree, in the hibiscus, or mallow, family (Malvaceae), widely planted as an ornamental for its showy flowers. It native to south China and Taiwan but widely introduced elsewhere, including much of Europe and North America. It was given the epithet syriacus because it had been collected from gardens in Syria.
Common names include the rose of Sharon,(especially in North America), Syrian ketmia, shrub althea (or simply althea, and rose mallow (in the United Kingdom). It is the national flower of South Korea and is mentioned in the South Korean national anthem.
History and Culture
Originally native to Korea, Hibiscus syriacus was introduced to Japan in the 8th century where it was cultivated for ornamental purposes. Historical records suggest that it thrived on the Korean Peninsula prior to the 1st century, with its leaves being utilized for brewing herbal infusions and its flowers consumed as food. The plant made its way to Europe by the 16th century, although concerns persisted regarding its hardiness.
Even as late as 1629, John Parkinson regarded it as delicate and recommended protective measures against winter weather. However, by the end of the 17th century, it became recognized as resilient, with some accounts describing it as hardy and suitable for outdoor cultivation. In the 18th century, it became a common fixture in English gardens and was also cultivated in North American colonies, where it was referred to as Althea frutex and “Syrian ketmia”.
Facts
| Scientific Name | Hibiscus syriacus |
| Other Common Names | Althea, Syrian Rose, Korean, Roserose mallow, Syrian mallow |
| Family | Malvaceae |
| Native Area | Eastern Asia, specifically China, Korea, and parts of Japan |
| USDA Zone | 5-9 |
| Flower Color | Varies (white, pink, purple, blue, red) |
| Flower Size | Typically 3-5 inches in diameter, but can vary |
Physical Description
- Rose of Sharon, is a deciduous shrub in nature.
- It grows to a height of 8-12 feet (2.4-3.7 meters) and spreads 6-10 feet (1.8-3 meters) wide.
- It features glossy leaves that are lobed and toothed, with a length of about 2-4 inches (5-10 centimeters). They are usually green or yellowish green. The leaves appear unusually late in the season, in May.
- The plant produces large, showy flowers with five overlapping petals in shades of white, pink, purple, or blue, often with a darker center. These blooms measure 2-4 inches (5-10 centimeters) in diameter and appear throughout the summer and early fall.
- The plant can bloom continuously from July through September, usually at night.
- The branches are thin and gray, white-lenticeled, with raised leaf scars and small buds. Stems and branches do not branch very much unless pruned.
- With maturity, flexible plant stems become weighted under the load of prolific summer flowers, and bend over halfway to the ground.
- Most modern cultivars are virtually fruitless. The fruits of those that have them are green or brown.
- It has no fall color but it can be stiff and ungainly if badly pruned.
- Full-grown plants can tolerate a wide range of conditions, including frost, drought and urban pollution.
Cultivars of Rose of Sharon
The following cultivars have gained the Royal Horticultural Society’s Award of Garden Merit.
| Cultivar | Common Name | Flower Color | Flower Type |
|---|---|---|---|
| ‘Blue Chiffon’ | ‘Notwood3’ | Blue | Semi-double |
| ‘Diana’ | – | White | Single |
| ‘Hamabo’ | – | Pale pink | Red center |
| ‘Lavender Chiffon’ | ‘Notwoodone’ | Pale lilac | – |
| ‘Meehanii’ | – | Pink | Variegated leaves |
| ‘Oiseau Bleu’ | ‘Blue Bird’ | Blue-violet | Maroon center |
| ‘Red Heart’ | – | White | Red center |
| ‘White Chiffon’ | ‘Notwoodtwo’ | White | Double |
| ‘William R. Smith’ | – | White | Single |
| ‘Woodbridge’ | – | Deep pink | – |
How To Grow and Care For Rose of Sharon
USDA hardiness zones
| USDA Zone | Temperature Range (°F) | Description |
|---|---|---|
| 5 | -20 to -10 | Requires some winter protection in colder areas. |
| 6 | -10 to 0 | Generally grows well with occasional winter protection. |
| 7 | 0 to 10 | Thrives with minimal winter protection. |
| 8 | 10 to 20 | Flourishes in relatively mild climates. |
| 9 | 20 to 30 | Does well in warmer conditions. |
- Location: Plant your Rose of Sharon in a location that receives full sun to partial shade. Ensure the area has well-draining soil to prevent waterlogging.
- Planting: Dig a hole twice as wide and as deep as the root ball of your Rose of Sharon plant. Place the plant in the hole, making sure the top of the root ball is level with the surrounding soil. Backfill the hole with soil and water thoroughly.
- Watering: Water newly planted Rose of Sharon regularly to help establish its roots. Once established, it is moderately drought-tolerant but benefits from consistent watering during dry spells.
- Fertilization: Apply a balanced fertilizer in spring to promote healthy growth and flowering.
- Pruning: Prune your Rose of Sharon in late winter or early spring to remove dead or damaged branches and to shape the plant. You can also prune for size control if needed. Avoid heavy pruning, as it may reduce flowering for the upcoming season.
- Mulching: Apply a layer of organic mulch, such as bark chips or compost, around the base of the plant to conserve moisture, suppress weeds, and moderate soil temperature.
- Pests and Diseases: Keep an eye out for common pests like aphids, spider mites, and Japanese beetles, which can occasionally bother Rose of Sharon. Treat infestations promptly with insecticidal soap or neem oil. Ensure good air circulation around the plant to prevent fungal diseases like powdery mildew and leaf spot.
- Winter Care: In colder climates, provide winter protection for your Rose of Sharon by applying a layer of mulch around the base of the plant and wrapping the shrub with burlap to shield it from harsh winds.
- Propagation: Rose of Sharon can be propagated from seeds, cuttings, or layering. Collect seeds from mature seed pods in autumn and sow them in spring. Softwood cuttings taken in summer can also root easily in moist soil.
Diseases and Pests
Diseases
Powdery Mildew
Powdery mildew is a fungal disease that appears as a white, powdery coating on the leaves, stems, and flowers of Rose of Sharon. It thrives in warm, humid conditions and can weaken the plant over time. To prevent powdery mildew, ensure good air circulation around the plant by spacing them adequately and avoiding overcrowding. Remove and destroy infected plant material, and consider applying fungicidal treatments early in the season as a preventive measure.
Cercospora Leaf Spot
Cercospora leaf spot is another fungal disease that affects Rose of Sharon. It causes dark brown to black spots with yellow halos to form on the leaves, eventually leading to defoliation if left untreated. To manage cercospora leaf spot, prune affected branches to improve air circulation and remove infected leaves promptly. Apply fungicides labeled for use on hibiscus plants according to the manufacturer’s instructions.
Botrytis Blight
Botrytis blight, also known as gray mold, is a fungal disease that thrives in cool, humid conditions. It causes brown lesions on the leaves, stems, and flowers of Rose of Sharon, often accompanied by a fuzzy gray mold. To prevent botrytis blight, avoid overhead watering, as the disease spreads through water droplets. Prune out infected plant parts and improve air circulation to reduce humidity around the plant.
Root Rot
Root rot is a common problem in Rose of Sharon caused by fungal pathogens such as Phytophthora and Pythium. It typically occurs in poorly drained soil or when plants are overwatered, leading to waterlogged roots. Symptoms include wilting, yellowing foliage, and eventual plant death. To prevent root rot, ensure the soil is well-draining and avoid overwatering. Plant Rose of Sharon in raised beds or containers if drainage is a concern.
Pests
Aphids
Aphids are small, soft-bodied insects that feed on the sap of plants, including Rose of Sharon. They can appear in large numbers, clustering on the undersides of leaves and along tender new growth. Aphid infestations can cause leaves to curl, yellow, or distort, and they may excrete a sticky substance known as honeydew, which can attract ants and promote the growth of sooty mold. To control aphids, spray affected plants with a strong stream of water to dislodge them, or use insecticidal soap or neem oil as directed.
Japanese Beetles
Japanese beetles are destructive pests that feed on the leaves, flowers, and fruit of Rose of Sharon, causing significant damage to the plant. These metallic green and copper-colored beetles can skeletonize leaves and leave plants looking ragged. Handpick adult beetles from plants early in the morning when they are less active, and consider using traps or applying insecticides labeled for Japanese beetle control.
Spider Mites
Spider mites are tiny arachnids that feed on the undersides of leaves, sucking sap from plant cells and causing stippling, yellowing, and premature leaf drop. These pests thrive in hot, dry conditions and can quickly multiply in large numbers, especially during periods of drought. To control spider mites, regularly inspect plants for signs of infestation, and use a strong stream of water to wash them off. In severe cases, consider applying insecticidal soap or horticultural oil.
Whiteflies
Whiteflies are small, moth-like insects that feed on the underside of leaves, sucking sap and excreting honeydew. They can cause leaves to yellow, wilt, and drop prematurely, and their sticky excrement can attract ants and promote the growth of sooty mold. To control whiteflies, use yellow sticky traps to monitor populations and reduce numbers, and apply insecticidal soap or neem oil as directed. Pruning heavily infested plant parts can also help reduce populations.