In several states rose of Sharon or altheas (Hibiscus syriacus) are classified as exotic (non-native) invasive shrubs (USDA hardiness zones 5-8). Their seedlings are invading U.S. woodlands. Plant breeders are now developing less invasive cultivars. The double-flowered altheas produce far fewer fertile seeds; stamens and pollen sacs are mostly embedded within the flower petals. Azurri Blue Satin® is […]