Blackeyed Susan vine (Thunbergia alata)

Overview

The Blackeyed Susan vine (Thunbergia alata) brings rapid, cheerful color to almost any garden structure during the warm season. This tropical evergreen twining vine is prized for its prolific display of distinctive orange-yellow flowers, each accented by a dark, characteristic “eye.” Gardeners value this plant for its vigorous growth habit, quickly covering trellises or cascading from hanging baskets.

Though native to tropical East Africa, Thunbergia alata is widely grown across temperate climates as a fast-maturing annual. In these regions, it typically reaches 3 to 8 feet tall within a single growing season, making it an excellent choice for temporary summer screening or vertical interest. Its adaptability to container life makes the Blackeyed Susan vine a versatile addition to patios and porches.

Beyond its aesthetic appeal, Thunbergia alata forms dense foliage that effectively covers supports, offering a lush, temporary backdrop for summer plantings. While frost-sensitive, its ease of propagation allows dedicated gardeners to preserve favorite specimens indoors through the winter, ensuring the return of this cheerful climber next spring.

Fast Facts

• Plant Family: Acanthaceae
• Plant Type: Vine
• Native Range: Tropical Africa
• Hardiness Zones: USDA Zones 10-11
• Size at Maturity:
  • Height: 3-8 ft
  • Spread: 3-6 ft
• Bloom Time: Seasonal bloomer
• Bloom Description: Orange-yellow
• Sun Exposure: Full sun to part shade
• Water Needs: Medium
• Maintenance Level: Medium

How to Grow

For the best establishment, sow Thunbergia alata seeds directly into the garden after all danger of frost has passed. Starting seeds indoors 6 to 8 weeks before your last expected frost date will ensure earlier blooming. Cultivate in organically rich, fertile, well-drained soil with consistent, medium moisture. While it tolerates full sun, providing some afternoon shade helps prevent stress during the hottest parts of the summer.

Watering for this tropical vine should be consistent; adequate moisture is necessary to support its rapid seasonal growth. Fertilization is generally not excessive; rich soil usually suffices, though a balanced liquid feed every few weeks during peak bloom can enhance flower production. Pruning is usually minimal unless you need to control size or shape it against a support structure.

In Zones 10-11, this plant can remain evergreen and overwinter outdoors. For gardeners outside these warm zones, treat the Blackeyed Susan vine as an annual. Alternatively, you can successfully take cuttings from mature plants in late summer and root them indoors to overwinter them in a bright, warm sunroom, ready to plant out again next year.

Landscape Uses

The primary value of Thunbergia alata in the landscape is its capacity for quick vertical development. It is perfectly suited for adorning trellises, arbors, and fences, adding dynamic height to borders or screening less attractive areas. The cascading nature of the plant also lends itself beautifully to hanging baskets or tall patio containers, allowing the vine to twist around supports or spill gracefully over the edges.

When planning container displays, pair the bright orange-yellow flowers of the Blackeyed Susan vine with trailing foliage plants or mounding annuals that can tolerate similar sun and water needs. Because it covers ground effectively, it can also function as a temporary annual ground cover in sunny summer borders where a fast-spreading texture is desired before perennial fillers mature.

Standout Features

Flower Qualities

• Showy

Noteworthy Characteristics

Thunbergia alata, commonly called black-eyed Susan vine, is native to tropical areas of East Africa. It is a tropical evergreen twining vine that eventually climbs to 20’ in frost free areas, though as an annual, it typically reaches 3-8’ tall in a single season. The plant features ovate-triangular toothed green leaves and solitary, axillary, salverform orange-yellow flowers up to 2” long, each marked with a distinct dark throat. Bloom time extends from summer into fall, often peaking after initial intense summer heat subsides.

Tolerances

Potential Problems

When grown indoors, particularly during overwintering, watch carefully for common houseplant pests. Scale insects, spider mites, and whiteflies are the most frequent intruders on the dense foliage of the Blackeyed Susan vine. Regularly inspect the undersides of leaves and treat immediately with insecticidal soap or horticultural oil to prevent severe infestations that could weaken the plant before the next growing season.

Frequently Asked Questions

What hardiness zones is Thunbergia alata suitable for?

This plant is winter hardy only in USDA Zones 10 through 11, where it grows as a tropical evergreen vine. Gardeners in cooler regions should plan to grow their Thunbergia alata as an annual.

How large does Blackeyed Susan vine grow?

As an annual in most climates, it reaches a height between 3 and 8 feet, with a comparable spread of 3 to 6 feet when given support. In frost-free environments, it can twine much higher, reaching up to 20 feet.

What sun exposure does Thunbergia alata need?

The Blackeyed Susan vine thrives best in full sun but appreciates some light afternoon shade, especially in very hot climates, to maintain its best performance and deep color.

When does Thunbergia alata bloom?

It is a seasonal bloomer, providing a consistent display of orange-yellow flowers, often reaching its peak performance in late summer and into the fall months.

Conclusion

The Blackeyed Susan vine (Thunbergia alata) is an incredibly rewarding annual for adding dynamic vertical texture and bright, reliable summer color to your garden. Its ease of cultivation via seed or cuttings, combined with its vigorous climbing nature, makes it a must-have for temporary screens or container accents. Before planting this season, confirm your local last frost date to time your seed starting perfectly for the best flowering display.

Propagation Tips

Since this vine is commonly grown as an annual outside of the tropics, knowing how to propagate cuttings is key to ensuring its return. In late summer, select healthy, non-flowering stems and take 4-6 inch cuttings just below a leaf node. Remove the lower leaves and place the cuttings in moist, well-drained potting mix, or use water/rooting hormone for faster results.

Keep the cuttings warm and maintain high humidity, ideally using a plastic dome or bag to create a mini-greenhouse effect. Once roots develop, the new Thunbergia alata plants can be potted up individually. These small plants can then be kept in a sunny window indoors throughout the winter months, providing mature stock for the following spring planting season.

Companion Planting

The vigorous growth and full sun needs of the Blackeyed Susan vine pair well with plants that enjoy similar conditions and provide contrasting foliage or flower shapes. Consider planting heat-loving partners such as zinnias, cosmos, or upright salvias nearby to create a vibrant, layered border. When using it in containers, pair it with cascading plants like sweet potato vine (Ipomoea batatas) or upright structural elements like small ornamental grasses.