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Thunbergia, also known as black-eyed Susan vine or clock vine, is a quick-growing vine boasting many open-faced flowers, usually with dark centers (hence the name "black-eyed Susan"). Where not struck down by frost it is a perennial, but most climates of the United States grow it as a beautiful annual. The name Thunbergia honors a Swedish botanist named Karl Pehr Thunberg.
: Black-eyed Susan vine can grow 6 to 8 feet tall in a season and has rough, hairy leaves. The blooms have 5 distinct petals and are symmetrical. Flower color can be white, yellow, orange, or cream. Most of them have dark centers.
: Generally, it grows best in full sun. It needs average, well-drained soil. Plant seedlings 3 inches away from supports. Space plants 5 to 8 inches apart. Pinch the tips to encourage branching. Since thunbergias climb by twining, netting or strings make good trellising materials. They will need a trellis to climb large posts or solid fencing.
: By seed or by cuttings. Sow seeds outdoors after the last frost or start seedlings indoors 6 to 8 weeks before outdoor planting. Seeds germinate in 10 to 15 days at 70 to 75 degrees Fahrenheit. Cuttings root easily in a commercial soil mix.
: Thunbergias can be used to cover posts, porches, arbors, pergolas, or fences. They also make good container plants. Plants in containers will also bloom over winter in sunny windows.
Thunbergia, black-eyed Susan vine, clock vine related species: Thunbergia gibsonii has somewhat larger flowers in a bright orange color. Thunbergia fragrans bears 2-inch wide, white, fragrant flowers. The most available variety is called Angel Wings and blooms in about 12 weeks from seed.
Thunbergia, black-eyed Susan vine, clock vine related varieties: Susie Mix is composed of orange, yellow, and white blooms, either with or without dark centers. African Sunset ranges from brick red to cream. Salmon Shades contains a variety of milky oranges.
: Thunbergia alata