Black-eyed Susan Vine, Thunbergia alata

Overview of Black-eyed Susan Vine

Thunbergia alata is a fast-growing, free-flowering vine. — *Thunbergia alata* is a fast-growing, free-flowering vine.

Black-eyed Susan vine is commonly grown in the Midwest as a vining annual to provide color in a vertical setting. Thunbergia alata is a tender evergreen perennial in the acanthus family (Acanthaceae) native from tropical East Africa to eastern South Africa that is hardy only in zone 9a and 10a. Despite sharing a the common name black-eyed Susan, it is completely unrelated to Rudbeckia hirta, an herbaceous annual or short-lived perennial in the daisy family (Compositae) native to north America. Because it grows and flowers quickly it is often used as an annual ornamental garden plant in cold climate areas. It should be grown with caution in frost-free regions, as it has become invasive in many warm locations throughout the world.

This trailing or twining vine grows rapidly from seed, reaching up to 8 feet in a single season under ideal conditions, but more often only 3 to 5 feet in the Midwest (and much more in frost free climates). The plant is a rambler, climbing by twining its stem around a support rather than by clinging or producing tendrils as some other vines do. The opposite, oval to triangular or heart-shaped leaves grow up to 3 inches long on winged petioles. They are soft and hairy, dull dark green on the upper surface and pale green with prominent veins below, with slightly toothed margins.

Showy flowers in shades of orange and yellow are produced singly in the leaf axils. Each 1½ inch wide flower emerges from a small yellow-green calyx enclosed in 2 large, ridged, hairy, green bracts. The trumpet-shaped corolla opens flat with five overlapping petals surrounding the brownish-maroon center.

Plants bloom from mid-summer to frost, often with the best display in late summer. The species typically has brilliant orange flowers, but there are cultivars in pastels and white as well. Butterflies, bees, and hummingbirds will visit the flowers.

This vine grows by twisting around supports (L) and had heart-shaped, softly hairy leaves (R). — This vine grows by twisting around supports (L) and has heart-shaped, softly hairy leaves (R).

Showy flowers (RC, from side and R from front) emerge (LC) from hairy bracts (L).

Pollinated flowers develop a fruit (LC) enclosed in the green bracts (L), which ripens and dries (RC) to a tan color.

Each fruit releases a number of reticulate seeds.

Seeds are often produced late in the season. The fruit resembles a bird’s head with a round base and a long “beak”. Each fruit contains 2 or 4 semicircular, reticulate seeds.

Landscape Use of Black-eyed Susan Vine

Black-eyed Susan vine will quickly cover small structures.

Black-eyed Susan vine does best when allowed to grow on a trellis or support structure instead of just rambling through adjacent plants, although it can be used as a ground cover. It makes a dramatic focal point when grown on a tall tuteur or other decorative support in a border or bed, will cover a fence, arbor, or trellis for decoration or to create a privacy screen, and will cascade from a hanging basket (as well as growing up the hanger!) Try combining black-eyed Susan vine with other aggressive vines such as morning glory or purple hyacinth bean. The orange or yellow flowers would contrast nicely with purple or blue flowers, such as salvia or ageratum, or purple-foliaged plants (such as Persian shield or purple heart) planted adjacent to the vine’s trellis. Use hot-colored flowers such as tall red zinnias, orange marigolds, or bright yellow celosia for a completely different look.

This vine will cascade down walls or from hanging baskets in addition to climbing.

Cultivars offer different colors than orange.

Or combine them with bright red cannas and large elephant ears for a tropical look.

White, orange and yellow Thunbergia alata in a large container. — White, orange and yellow *Thunbergia alata* in a large container.

This vine can be used in a large container with a small trellis, and can be grown as an indoor plant (although it will likely need to be trained and pruned to keep it at a manageable size). Plants in containers will bloom over winter if kept in a sunny place and night temperatures are above 60 °F.

In frost-free climates this vine is perennial and will grow very dense.

The vine will quickly fill narrow vertical spaces with color.

Thunbergia alata grows best in fertile, moist soil in full sun. It tolerates partial shade but flowering may be reduced.

Plants grown in containers can be overwintered indoors in a warm, very bright room.

Propagating Thunbergia alata

This plant is most commonly propagated from seed (although softwood cuttings can be taken or stems layered, too, but plants grown from seed tend to be more vigorous). Start seeds indoors 6 to 8 weeks before the average last frost, and plant outside once all danger of frost has passed and night temperatures remain above 50 °F. Soaking the seeds in warm water overnight before sowing will speed germination. Press the seeds into the soil, covering completely. Seeds should germinate in 10 to 21 days.

Seed can be sown directly where the plants are to be grown once soil temperature reaches 60 °F in the spring, but transplants give better results in the short growing season of the upper Midwest. Transplant near a trellis, fence, or other support structure, 14 to 16 inches apart. Fertilize every 2 to 3 weeks when in bloom if grown in containers. Outdoors black-eyed Susan vine has few pest problems, but if grown indoors it is often infested by spider mites and whiteflies.

Black-eyed Susan vine is most often propagated from seed.

There are many different.cultivars available.

Cultivars of Thunbergia alata

Often just the basic orange type is offered for sale as plants or seeds, but there are many cultivars. Some of the more common or interesting ones available include:

‘African Sunset Mix’ is a seed propagated cultivar featuring flowers in shades of apricot, buff, and red, all with dark eyes. Vines grow to 5 feet.
‘Amber Eyes’ has large amber yellow flowers with large dark eyes and vines grow to 5 feet.
A-Peel® collection from Proven Winners® features vigorous plants with large flowers and vines that reach 5 to 8 feet long. Available in Lemon (variety ‘Lemon Star’), Orange (variety ‘Orange Wonder’, also in the Sunny™ collection), Coconut (variety ‘VOLTHU 9327’ US PP 33,361), and Tangerine Slice (variety ‘DL1501’ US PP 30,215), with rusty orange flowers with yellow edges and dark eyes.
‘Blushing Susie’ is a mix in shades of apricot and rose and dark centers
‘Bright Eyes’ has all white flowers
‘Pure White’ features pure white flowers
‘Raspberry Smoothie’ has pale lilac-pink flowers and greyish green foliage
‘Spanish Eyes’ is a mixture of flower colors in more muted shades of apricot, terra cotta, salmon, rose and ivory, all with a dark centers.
Sunny™ collection is a vigorous, large flowered, floriferous, vegetative series with vines that grow 6 to 8 feet long. It includes Arizona Glow (variety ‘VOLTHU 1007’), with red-orange flowers with dark eyes, Rose Sensation (variety ‘VOLTHU 7898’, US PP 29,733), with rose flowers with dark eyes, ‘Lemon Star’, with bright yellow flowers, and ‘Orange Wonder’, with vibrant orange flowers with dark eyes.
‘Superstar Orange’ has extra large, bright orange flowers
‘Susie Mix’ features orange, yellow, and white flowers with and without dark eyes. Vines grow to 7 feet.