Plant Profile: Rose of Sharon / Althea (Hibiscus syriacus)
- Judith Paul
- Oct 16
- 4 min read
These shrubs work hard over summer, producing bloom after bloom, often to the point where it’s hard to see the foliage. Hummingbirds and pollinators love them, taking advantage of the nectar from early summer through to when the first frosts send them into their winter hibernation.
Rose of Sharon (ROS) and Althea are the common names usually associated with this shrub in America. In Italy, they are known as St Joesph’s Rod, and as Mukuge in Japan. They are native to east-central and southeast Asian countries, which include China, Korea, and India, but the botanical name ‘Hibiscus syriacus’ provides us with other possibilities, including Syria. Regardless of where they originated, the countries associated with their origin give you some idea of just how tough and adaptable they are!
Some people also refer to them as Rose Mallow, but in my opinion, that common name confuses them with ‘cousins’ that have different characteristics. They are also often referred to as hardy hibiscus. This is a misleading term that is often also used in conjunction with the group of hibiscuses that are herbaceous perennials, i.e. they do the ‘dead stick’ thing in winter and regrow from their roots in spring. They are winter hardy from Zones 5 – 9/10 and can be planted in full sun to part-shade locations.
They’re not fussy about soil types, including clay, though amending the soil with pine fines and/or compost will help them get established. Once established, watering is not essential, but blooms and growth will be better if given a good soak once a week during particularly hot and dry weather.
Maintenance is minimal. If you feel the need to do so, just shape them to your preferred height and width over winter when they’ve dropped their leaves. Winter pruning enables you to see the structure of the plant, and that makes it easier to see which branches need attention. That includes branches that are crossed as well as those that should be removed from the center to open it up for some airflow during summer, when it is often densely leafed out and covered in blooms.
The older varieties of the Rose of Sharon have a reputation for aggressive self-seeding. Removing seedlings each spring can be a tiresome job, and there are also concerns about seed ‘escaping’ and invading native habitat. This is less of a concern now when selective breeding has resulted in cultivars that do not produce fertile seed. Some examples of these infertile cultivars are listed below.
One of the other wonderful features of this type of hibiscus is that it is quick-growing. Within a few years, a 2 to 3-gallon plant will be approaching full height and starting to branch out. Compared to a Japanese Maple, they are phenomenally quick!
These versatile shrubs can be used in many different garden styles. My favorite is as a focal point in a cottage garden or towards the back of a mixed border, but they can also be stand-alone specimens, trained into tree form, or lined up as a deciduous hedge. Hibiscus syriacus ‘Morning Star’ is a vigorous grower that can get up to 12’ high in ideal conditions, so you can put it at a considerable distance from the house and still enjoy it. Their usual height is more like 6-8" with a width slightly less. This is one of the varieties that is recommended for hedges and shaping into a tree form. It has a pure white, ruffled bloom with a crimson throat. Stunning!
Hibiscus syriacus ‘Ardens’ has vibrant green foliage that sets off the elegant, lavender shade of the 3" ruffled blooms with a maroon splash of color at the center. In autumn, the leaves take on a slight yellowish hue. This is another one that can get quite large at 12’ H x 8’ W, and it is also one of the most shade-tolerant.
Hibiscus syriacus ‘Blue Bird’ is considered the best blue-flowered variety. It produces an abundance of showy violet-blue single blossoms with a darker eye. The upright, vase-shaped habit with handsome foliage makes it an ideal shrub for use as a hedge, foundation plant, or specimen plant, providing reliable summer color. This one is slightly smaller at 6-8’ H x 6’ W.
Hibiscus syriacus ‘Amplissimus’ produces 2-3" wide, double, purplish-red flowers throughout much of summer. As with all H. syriacus, this is an easy-to-grow, vigorous shrub that is particularly tolerant of heat and average soil conditions. It tops out at 8-10ft H x 6-8ft W and with a strongly upright habit.
Hibiscus syriacus ‘Collie Mullens’ produces large rose-pink to lavender-purple, semi-double flowers showcased beautifully against glossy foliage. It has a particularly elegant upright habit up to 10’ H but only 6’W.
Hibiscus syriacus ‘Aphrodite’ has pink and red bi-tone blooms up to 4” in width (sometimes more). With its highly serrated and very dark green leaves, the foliage is particularly ornate and a wonderful backdrop to the blooms.
Hibiscus syriacus ‘Diana’ also produces very large blooms up to 4” wide, and the blooms are pure white. Plant one of these near a plant with a contrasting color that blooms at the same time to enjoy the full effect! At 8ft H x 6ft W, ‘Diana’ is suitable for smaller yards.
Hibiscus syriacus ‘Sugar Tips’ is a most unusual Rose of Sharon because it is one of the few that has variegated leaves, which are a soft, sage green with a creamy-white edge. The petals on the flowers are a blush pink, with a contrasting maroon center. Officially known as a semi-dwarf, it only gets 5-6ft H&W and could be container-grown.
Article by
Judith Paul
Hi, I'm Judith Paul, with a gardening style best described as “Oooo, there’s a gap over here!” My work history is equally unpredictable (possibly even quirky) and ranges from pulling eel-infested cow carcasses out of creeks to managing multi-million-dollar projects across various industries. I’m a Kiwi (referring to the iconic flightless bird of NZ, not the fruit) who has also lived in Australia. Currently, I run a licensed and inspected plant propagation nursery in North Carolina (USA) when I’m not teaching, writing, or editing.
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