A vigorous, twining tender climber. Suitable for warm sheltered gardens. Usually grown as an annual in the UK. The prolific showy flowers stand out well against its rich green leaves in summer.
Botanical Name: Thunbergia
Common Names: Black-eyed Susan, bright eyes, clock vine.
Foliage: Evergreen, heart-shaped or oval toothed leaves.
Flowers: Five petal open trumpet-shaped flowers. Usually orange/yellow with a dark centre. Often followed by pea-sized winged seed capsules.
Flowering Period: June to September.
Soil: Moist but well-drained soil (chalk, clay or loam). Acid, alkaline or neutral pH.
Conditions: Full sun. Plant in a west or south facing aspect, in a sheltered location.
Habit: Spreading, climbing, self-clinging.
Type: Half-hardy Annual.
Origin: Africa and Asia.
Hardiness: Tender in UK, protect from frost.
Easy-to-grow and low-maintenance with a long flowering season. Thunbergia is good conservatory perennial, which is less demanding that other tender plants.
Can also be grown as an annual outside, against a warm sheltered sunny wall, fence or pergola. Plant in a humus rich, fertile, well-drained soil.
Provide support wires, canes or netting for the stems to twine round. Black-eyed Susan can quickly cover a small area within a single growing season. They will also trail, making them ideal for large baskets and containers.
Water well during dry spells. Feed every few weeks with a liquid fertilizer for flowering plants.
Not necessary. Pinch off the growing tips to control height and spread. Pull up and discard annuals to the compost heap once flowering has finished.
Susceptible to attack by Aphids and other glasshouse pests if grown under glass. Can be affected by powdery mildews.
Sow in early spring under glass, in individual pots of seed compost. Harden off before planting out at the end of May. Alternatively, sow in a well prepared seed bed, where they are to flower, around late April-May.
Thunbergia alata (black-eyed susan) is a twining plant with heart shaped, mid green leaves and striking orange-yellow flowers, with a dark brown or purple centre. Height up to 10ft (3m), spread 1.5ft (45cm). Cultivars include:
Thunbergia fragrans 'Angels Wings' yellow flowers with a white eye.