Also known as clock vine and blue trumpet vine, sky flower (Thunbergia grandiflora) produces clusters of 3-inch blue or violet, yellow-throated flowers. At first glance, one could mistake its trumpet-shaped flowers for smaller morning glory blossoms. Its heart-shaped, fuzzy, dark green leaves grow up to 8 inches long and 4 inches wide. In some warm regions, such as Queensland Australia, this woody vine grows up to 30 feet long in its lifetime or 8 feet in one season, and is considered an invasive weed.
Geography
Native to India, sky flower thrives in warm climates where the temperature does not drop below freezing. It grows outdoors in United States Department of Agriculture (USDA) Zones 8 to 11, and can overwinter indoors or grow as a houseplant in cooler climates. The plant tops will die back at sub-freezing temperatures, but the roots will generate new growth in the spring. Sky flower has a low tolerance for the salt spray found in Florida and other coastal regions.
Site Requirements
In the garden or in a container, sky flower vines grow well in moist, well-drained soil that is high in organic content. Although it tolerates brief dry periods, this moisture-loving vine needs water every 10 to 14 days to maintain even soil moisture. Outdoor plants flower profusely in a sunny area, but prefer afternoon shade in a hot climate. Sky flowers need a trellis, pergola or other structure to support its rapid growth.
Time Frame
Although sky flower is a perennial evergreen in warm climates, it grows rapidly enough to serve as an annual vine in cooler regions. The showy flowers provide a colorful display from summer to fall. Propagate this vine from cuttings during warm weather, or plant seeds indoors six to eight weeks before your area’s last anticipated frost date. To ensure adequate nutrients, add a balanced fertilizer, such as 10-10-10, in early spring and early summer. Prune away dead plant material after the first freeze, and prune back stems any time to control vigorous growth.
Pests
Tiny whiteflies, scales and spider mites occasionally attack sky flower vines and cause yellow leaves, leaf drop and plant death. Yellow or green spider mites, which are barely visible to the naked eye, feed on leaf and stem sap. Brownish scales and moth-like whiteflies measure 1/16 inch long and suck sap from the undersides of leaves. You can remove light infestations by hand or with water, or control heavy infestations with horticultural oils and insecticides such as permethrin and bifenthrin. Move a houseplant outdoors before applying chemical pesticides and follow label instructions carefully.
Jack Scheper, “Thunbergia grandiflora”, Floridata
Jeffrey Hahn, Deborah Brown and Mark Ascerno, “Houseplant Insect Control”, University of Minnesota Extension
Tom MacCubbins, “Plant Profiles — Bengal Clock Vine”, University of Florida IFAS Extension