HOW TO GROW ROSE OF SHARON & OTHER HARDY HIBISCUS VARIETIESBring the tropics to your garden with these plants that can overwinter even in temperatures below zero
Hibiscus plants aren’t only for the tropics. In fact, some hardy hibiscus varieties, like the popular rose of Sharon, can overwinter outdoors in temperatures as cold as 20° below zero.
There are two popular types of hardy hibiscus, with the main distinction being size—of both the plant and the flower.
- Rose of Sharon: Larger shrubs that produce abundant smaller flowers.
- Mallow varieties: Smaller shrubs, but produce large, dinner-plate-size flowers.
Although the 2 types differ in size, much of their growing and care requirements are the same.
Generally 5-9, with some exceptions.
Rose of Sharon varieties can grow 8-12 feet tall and 6-10 feet wide. Mallow varieties are typically between 3-5 feet tall and 2-4 feet wide; however a few mallows can reach heights of 10 feet.
Full sun to partial afternoon shade (best flowering in full sun).
Prefers moist, yet well-drained, acidic soil; mulch to help retain moisture.
Mallow varieties will start blooming in June, with rose of Sharon varieties following a little later in July; both will bloom into fall or until first frost.
Shades of white, pink, red, and purple; sometimes with a contrasting throat.
Both varieties are deciduous; with medium-green, heart- or maple-shaped leaves, although there are a few exceptions.
Hardy varieties are also known as rose of Sharon, rose mallow, swamp mallow, or althea.
When to plant:
Rose of Sharon and other hardy hibiscus varieties can be planted in spring or fall, as long as there is no danger of frost.
Where to plant:
Full sun to partial afternoon shade. An area with good air circulation produces the best flowers and strongest stems, and is the best environment to prevent disease. Keep an eye out for hot, scorching afternoon sun that may burn the foliage; as well as provide protection from damaging wind.
How to plant:
Seeds can be started indoors and then transplanted, but it is more common to plant potted plants purchased from a nursery. Dig a hole twice the width of the pot and set the plant in. Make sure the crown of the plant rests just at or above the soil line. Backfill the hole, and water well.
Hibiscus need a fertilizer high in potassium (K), low in phosphorus (P), and with a medium amount of nitrogen (N) - too much phosphorus will kill a hibiscus. Hibiscus also respond well to an organic fertilizer, and a good layer of compost once a year is generally sufficient. Don’t fertilize after July as this can push new growth that will be damaged by frost.
They prefer moist soil and do not tolerate drought. They should be watered regularly and up to twice a day in hotter weather, especially if being grown in a container. Watering can be cut back a bit in colder weather. Water-stressed hibiscus may drop their buds or become more susceptible to insects and disease. They should not be left in standing water as this can promote root damage/root rot.
When properly planted and cared for, you can get many flowers from one hardy hibiscus plant (shown is a type of Hibiscus moscheutos). Photo by: billysfam / Shutterstock.
Little actual pruning is required, and is generally only needed to maintain appearance, size, and shape. They can be cut back 4-6 inches from the ground in spring, anytime before the new growth emerges. Stems are quite woody and you may need heavy loppers or possibly a saw. Pruning before very cold temperatures or in extreme heat can be very stressful to your plant and do more harm than good. Tip pruning can stimulate branching, and since more branching means more flowers, a little trim late spring to early summer can be a good thing.
Hibiscus may re-seed abundantly, and plucking new hibiscus from areas where they are not wanted may become a new chore. To help prevent an over-abundance of seed pods from forming, remove dead blooms from your hibiscus (deadhead) in mid-to-late fall.
Hardy varieties will die back to the ground in the winter in colder regions, but new growth will develop in spring from the root tops. Don’t panic however, as hibiscus are one of the last to show new growth. In colder climates, cover the root ball with mulch to insulate it. Some varieties require freezing to promote new growth.
Diseases and Pests:
Hardy hibiscus can fall prey to a number of pests, including Japanese beetles, whiteflies, aphids, and ants. Ants can be more than a mere annoyance on your hibiscus, as they will actually bring aphid eggs to the hibiscus so that they can feed off of the byproducts the aphids produce from sucking the sap from the leaves and flowers.
Keeping your hibiscus healthy, free of pests, and in an area with good air circulation are the best defenses against disease. Hibiscus may be susceptible to dieback disease, wilt disease, and leaf fungus.
Blue Chiffon® — Buy now from Proven Winners
Rose of Sharon
Height/Width: 8-12 feet tall, 4-6 feet wide
This blue-flowered selection grows vigorously, with a rounded habit. Flowers have a fluffy center and produce few seeds. Provides beautiful blue late summer color in the garden.
Awarded 2020 Flowering Shrub of the Year by Proven Winners. "Its impressive size, refined shape and durable nature make Blue Chiffon an ideal foundation plant when establishing or renovating a landscape design."
Summerific® 'Berry Awesome' — Buy now from Proven Winners
Rose mallow hybrid
Height/Width: 40-48 inches tall, 54-60 inches wide
Large ruffled flowers, up to 8 inches across, bloom all over this densely compact shrub from mid-summer to early fall. Deadheading isn't necessary, but will keep the plant looking its best. Chosen as Proven Winners' 2019 Perennial of the Year.
Summerific® 'Cranberry Crush' — Buy now from Proven Winners
Rose mallow hybrid
Height/Width: 36-48 inches tall, 48-60 inches wide
A dense, naturally compact shrub. Large scarlet red flowers that are 7 to 8 inchess across bloom atop deep green leather foliage. Blooms originate from nodes all up the flowering stems, not just at the top like others.
Summerific® 'Holy Grail' — Buy now from Proven Winners
Rose mallow hybrid
Height/Width: 48-54 inches tall, 54-60 inches wide
Deep red flowers are set against incredibly dark (nearly black) foliage on this hardy hibiscus. Perfect as a show-stopping mid-to-late-summer focal point.
Purple Pillar® — Buy now from Proven Winners
Rose of Sharon
Height/Width: 10-16 feet tall, 2-3 feet wide
A unique variety that grows tall and narrow, instead of wide, making it a great choice for privacy screening, hedging, containers, or any narrow space. Semi-double, purple flowers bloom along the entire length of the stems. The fact that it has few branches means little to no pruning is needed.
Sugar Tip® Gold — Buy now from Proven Winners
Rose of Sharon
Height/Width: 48-60 inches tall and wide
Another cultivar that produces far fewer seeds than standard varieties, making it nearly maintenance free. This rose of Sharon has variegated foliage and light purple, double flowers.
Rose of Sharon
Height/Width: 6-8 feet tall and wide
Blooms mid-summer to frost with 3 to 5-inch violet-blue flowers that have red throats.
Height/Width: 6-15 feet tall, 6-10 feet wide
This hibiscus blooms late summer through fall, bringing late season color to gardens. Its large blooms open white and turn pink through the course of the day.
H. x moscheutos
Height/Width: 3-4 feet tall and wide
A compact rose mallow hybrid, ‘Kopper King’ features copper-red foliage and pink flowers up to 12 inches across.
Height/Width: 4-6 feet tall, 2-3 feet wide
This selection has striking green foliage that develops to a purple color in full sun. A good choice for gardens with extreme heat and humidity.
‘Blue River II’
Height/Width: 4-5 feet tall and wide
This hybrid cultivar has deep green leaves, with a tinge of blue. Great for use in a night garden.
- Mallow varieties are native to swampy areas and can be useful in low spots or wetter areas, along streams or ponds.
- Excellent foundation planting, anchoring structures to the landscape; planting close to buildings also provides some cold protection for the plant.
- Hibiscus are some of the most colorful plants in the landscape, especially mallow varieties with their large blooms, so be careful not to overwhelm an area or have clashing tones.
- Rose of Sharon, generally multi-trunked shrubs, can be trained as a single-trunk ‘tree’ or espalier.
- Hardy hibiscus are not good for cut flowers, as their blooms only last a day or two. Their dried seed pods can provide an exotic look and last longer in an arrangement.
IS ROSE OF SHARON INVASIVE?
Hibiscus syriacus can be invasive in the following areas:
- Most of Indiana
- Parts of the South
- Coastal areas of the Mid-Atlantic
To see if rose of Sharon is invasive in your area check out this map from InvasivePlantAtlas.org.
If you're in love with this plant, but don’t want to worry about it reseeding, try selections from the Summerific® series from Proven Winners.
Last updated: July 29, 2020