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Rose of Sharon, Shrub Althea 'Tosca'

Hibiscus syriacus

Family: Malvaceae (mal-VAY-see-ee) (Info)
Genus: Hibiscus (hi-BIS-kus) (Info)
Species: syriacus (seer-ee-AK-us) (Info)
Cultivar: Tosca
» View all varieties of Hibiscus


8-10 ft. (2.4-3 m)


24-36 in. (60-90 cm)

36-48 in. (90-120 cm)

4-6 ft. (1.2-1.8 m)


USDA Zone 5a: to -28.8 C (-20 F)

USDA Zone 5b: to -26.1 C (-15 F)

USDA Zone 6a: to -23.3 C (-10 F)

USDA Zone 6b: to -20.5 C (-5 F)

USDA Zone 7a: to -17.7 C (0 F)

USDA Zone 7b: to -14.9 C (5 F)

USDA Zone 8a: to -12.2 C (10 F)

USDA Zone 8b: to -9.4 C (15 F)

Sun Exposure:

Sun to Partial Shade

Bloom Color:

Magenta (Pink-Purple)

Bloom Time:

Mid Summer

Late Summer/Early Fall



Other details:

Unknown - Tell us

Soil pH requirements:

Unknown - Tell us

Patent Information:

Unknown - Tell us

Propagation Methods:

From woody stem cuttings

Seed Collecting:

N/A: plant does not set seed, flowers are sterile, or plants will not come true from seed

Foliage Color:

Unknown - Tell us

Bloom Characteristics:

This plant is attractive to bees, butterflies and/or birds

Water Requirements:

Average Water Needs; Water regularly; do not overwater

Where to Grow:

Unknown - Tell us


This plant has been said to grow in the following regions:

Warren, Michigan

Gardeners' Notes:


On Jun 17, 2013, Dean48089 from Warren, MI (Zone 6b) wrote:

The entry for this plant is somewhat misleading. Hibiscus 'Tosca' is a hybrid between our native Hibiscus paramutabilis and Hibiscus syriacus, possessing features from each parent. I first bought 'Tosca' and 'Lohengrin' at the same time from Glasshouse works about 13 years ago. I planted them in a spot expecting growth similar to H. syriacus, which is a slow grower in my heavy clay soil. By their third summer both 'Tosca' and 'Lohengrin' were over twelve feet tall and at least six feet wide, overwhelming all their neighbors. So I cut them both down to 2' stumps with the intention of letting them grow back in a more controlled manner. 'Tosca' did not appreciate this treatment and the stump died. Fortunately, taking after its H. paramutabilis parent, the plant sends up the occasional ... read more