Tips for Growing Althea
Rose of Sharon will help bring a bit of tropical beauty to more temperate climates. The blooms that arrive later in the summer will help revive your garden after the flurry of spring flowers.
Latin name: Hibiscus syriacus
Common Names: Rose of Sharon, Althea, hardy hibiscus
USDA Hardiness Zones: Zones 5-8
Size & Shape of Rose of Sharon: Rose of Sharon grows to approximately 8-12' tall and 6' wide, with a vase shape.
Exposure: It is best to grow Rose of Sharon in full sun, though it can tolerate up to part shade.
Foliage/ Flowers/Fruit of Rose of Sharon:
Don't be surprised if the leaves arrive after most of your other plants, as they start producing the leaves late in spring. Leaves are 2-4" long, often with 3 lobes, and jagged edges.
The flowers are 2-5" wide, in shades of white, pink, red, blue, purple, and violet. There is often a different spot of color in the middle of the throat.
Close relatives include Cotton. Okra. Mallow. Marsh mallow (marshmellow). Cotton Boll pictured, Left.
Additional Rose of Sharon Facts:
Rose of Sharon can be VERY invasive due to the numerous seeds produced in the capsules. Snip them off before they open. This causes many to re-bloom!
Choose one of the newer cultivars that are genetic hybrids - the triploids. These produce few (if any) seed capsules.
Cultivars from the U.S. National Arboretum include:
2 faves are 'Blue Angel' and 'White Angel'
The blossoms are edible*. (*Colorado State Cooperative Extension Service)
In the UK and Australia, Rose of Sharon refers to Hypericum calycinum, which Americans know as St John's Wort.
Rose of Sharon Design Tips:
Leaves appear late in spring and the blooms do not show until late summer or early fall, so best used in a border, rather than as a specimen plant.
Rose of Sharon is somewhat tolerant of drought conditions.
Rose of Sharon Growing Tips:
Rose of Sharon grows best in moist, well drained soil that contains lots of organic matter, though happily it is able to tolerate a wide variety of soils.
In the cooler zones (where the temperatures fall below -10F in winter), be sure to mulch around the plant well during the winter season.
With hot summers, Rose of Sharon will thrive, actually preferring the heat, and will increase numbers of blooms.
Propagation is by cuttings and seeds.
Though it is naturally a multi-stemmed shrub, Rose of Sharon can be trained to have a single trunk, looking more like a tree. It can also be trained as an espalier or shaped into a hedge.
Prune as needed to maintain the shape desired. In winter or early spring, last season's growth should be pruned away, which will help produce bigger blooms.
Pests & Diseases of Rose of Sharon:
Unfortunately, Japanese Beetles love the Rose of Sharon shrub. Other pests include aphids and spider mites.
Diseases include leaf spot, blight, and cankers.
The buds may drop if the plant is watered too much or too little, or if too much fertilizer is applied.
Pink Tropical Hibiscus (close relative) is pictured above left.