How to Grow Thunbergia – Black-Eyed Susan Vine

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Thunbergia–commonly called black-eyed Susan vine–is a perennial climber usually grown as an annual. Bright yellow to orange five-petaled flared tubular flowers with dark eyes grow above bright-green, triangular leaves.

Other vines among the Thunbergia genus are the orange clock vine and sky flower. Both are grown in the same manner as black-eyed Susan vine.

Thunbergias are perennials but they are commonly grown as annuals. In mild winter regions, some will bloom year-round.

Flowering Thunbergia trained on a wooden trellis
Flowering Thunbergia trained on a wooden trellis

Get to know Thunbergia

  • Plant type: Tropical perennial vine grown as an annual
  • Growing Zones and range: Zones 10-11 as a perennial; all zones as an annual
  • Hardiness: Grow as an annual in Zones 2-9; grow as a perennial in Zones 10-11
  • Height and width: 6 to 10 feet (1.8-3m) tall and wide
  • Foliage: Triangular bright green leaves
  • Flowers:  Flaring tubular or tunnel-shaped flowers 1-inch in diameter
  • Flower colors: Yellow, orange, or creamy white with dark centers
  • Bloom time: Early summer until fall
  • Uses: Covering trellises, lattice, small fences; use to trail over the sides of hanging baskets and other containers
  • Common name: Black-Eyed Susan Vine
  • Botanical name: Thunbergia alata
  • Family: Acanthaceae
  • Origin: Southern Africa

Where to plant Thunbergia

  • Plant Thunbergia in full sun. In hot summer regions, plant in a spot that receives partial shade in the afternoon.
  • Grow Thunbergia in humus-rich, well-drained soil.
  • Thunbergia prefers a soil pH of 6.8 to 7.7.

Thunbergia uses

  • Thunbergia is decorative on fences and trellises.
  • Dwarf forms are attractive trailing from hanging baskets and window boxes.
 Black-eyed Susan vine, Thunbergia alata
Black-eyed Susan vine, Thunbergia alata

When to plant Thunbergia

  • Set established seedlings or sow seeds directly in the soil in late winter or spring after all danger of frost has passed.
  • Sow Thunbergia seeds indoors 6 to 8 weeks before the last frost in spring. Sow seed at 60° to 70°F ( 15.6°-21°C).
  • Germination takes 14 to 21 days.

Planting and spacing Thunbergia

  • Sow Thunbergia seed 1/8 to 1/4 inch deep in sterile potting mix or evenly prepared garden soil.
  • Space Thunbergia 6 to 10 feet (1.8-3m) apart.

How to water and feed Thunbergia

  • Thunbergia needs ample moisture; keep the soil evenly moist.
  • Fertilize Thunbergia with a slow-release fertilizer in spring.
Sky flower vine, Thunbergia grandiflora
Sky flower vine, Thunbergia grandiflora

Thunbergia care

  • Mulch around Thunbergia to conserve soil moisture.
  • Once they are about 1-inch high, thin plants to at least 12 inches apart.
  • Vines climb by twining; support can include trellises, string-trellises, teepees, lattice, chain link fencing.
  • In Zones 2-9, remove plants after frost or when it gets ragged in early winter. In Zones 10-11, frost will kill to the ground, but plants will reemerge.
  • Vines are very sensitive to frost; protect roots with mulch.
  • Over-wintered plants are more vigorous than first-year plants.
  • Prune in spring before new growth begins.

Growing Thunbergia as a houseplant

  • Thunbergia alata can be grown as a houseplant.
  • Grow Thunbergia in a room where the temperature is average to warm, light is direct and humidity is average.
  • The growing medium should be soilless and well-drained; keep the soil constantly moist when the plant is flowering. At other times, let the medium dry out slightly between waterings.
  • Fertilize thunbergia every two weeks during spring and summer.
  • For vines, provide a trellis or other support, or let plants cascade out of hanging baskets.

Thunbergia pests and diseases

  • Mealybugs and scale insects can attack Thunbergia.

Thunbergia propagation

  • Sow Thunbergia seed in spring.
  • Seed germinate in 14 to 21 days at 70° to 75°F (21°-24°C).
  • Take cuttings in summer. Use cutting to propagate and overwinter plants for setting in the garden the following spring.
  • Thunbergia can be propagated by layering.
Flower of orange clock vine, Thunbergia gregorii,
Flower of orange clock vine, Thunbergia gregorii,

Thunbergia varieties to grow

  • Thunbergia alata, black-eyed Susan vine: Perennial vine is grown as summer annual; small trailing, twining vine with triangular leaves; flowers are flaring tubes to 1 inch wide in orange, yellow, or white, all with a purple-black throat. ‘Susie’ series is the most popular; flowers are yellow, orange, and cream with dark centers. ‘Alba’ has white flowers wiht dark centers. ‘Aurantica’ has orange-yellow flowers with dark centers. ‘Bakeri’ has pure white flowers.
  • T. erecta, King’s mantle: Evergreen shrubs to 6 feet tall, erect, sometimes twining; dark green leaves; dark blue flowers with orange or cream throats in summer and fall.
  • T. grandiflora, sky flower: Perennial vine grows to 20 feet; heart-shaped leaves; slightly drooping tubular flowers 3-inches across in pure blue; blooms summer to fall.
  • T. gregorii, orange clock vine: Perennial grows to 6 feet tall; toothed 3-inch leaves; flaring tubular bright orange flower; blooms nearly all year in mild regions, in summer where winters are cold; can be grown as ground cover.
  • T. mysorensis: Perennial one with hanging clusters of red and yellow flowers; blooms in summer; train to a pergola for the best display of flowers.

Written by Stephen Albert

Stephen Albert is a horticulturist, master gardener, and certified nurseryman who has taught at the University of California for more than 25 years. He holds graduate degrees from the University of California and the University of Iowa. His books include Vegetable Garden Grower’s Guide, Vegetable Garden Almanac & Planner, Tomato Grower’s Answer Book, and Kitchen Garden Grower’s Guide. His Vegetable Garden Grower’s Masterclass is available online. has more than 10 million visitors each year.

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