The black-eyed Susan vine (Thunbergia alata) trails over fences and trellises, creating a dramatic display of color with its bright blooms. These simple flowers feature five petals with a dark center that resembles an eye, giving rise to its name. Traditional blooms range from yellow to orange, but new cultivars exist in shades of pink, apricot and peach. Although it is winter hardy in U.S. Department of Agriculture plant hardiness zones 10 through 11, it it typically grown as an annual in cooler climates.
Light and Soil
The black-eyed Susan vine thrives in full sun to partial shade. It performs well in locations where it receives full sun in the morning with some afternoon shade to shield it from the hot afternoon rays. It needs fertile, well-drained soil, which means you should add 1 to 2 inches of peat moss, finished compost or well rotted manure to the soil before planting. Work the organic matter into the top 6 inches of soil to improve aeration and drainage and provide plants with slow-release nutrients.
Black-eyed Susan vines are sensitive to the cold and must be transplanted to the garden after all danger of frost has passed in your area. Space the seedlings 12 to 24 inches apart when planted in the soil or add one to two vines to hanging baskets and window boxes.
Watering and Fertilizing
The black-eyed Susan vine performs best in evenly moist soil and benefits from a 2- to 3-inch layer of organic mulch to conserve moisture. Water vines once or twice a week to moisten the soil to the root level or whenever the soil feels dry 1 inch below the surface or the vines show signs of wilting. When the soil begins to dry, these vines may wilt profusely during the hottest part of the day and revive quickly once the sun sets. The black-eyed Susan vine may benefit from light fertilizing once or twice during the summer. Mix water-soluble fertilizer designed for flowering plants at a rate of 1/2 tablespoon per gallon of water. Too much fertilizer causes the vine to produce lush foliage but inhibits blooming.
Deadheading and Pruning
When grown as perennials, black-eyed Susan vines can reach a height of 20 feet, but as an annual it rarely grows more than 5 to 6 feet. Pruning to shape and control the height of the plant can be done at any time. Disinfect blades on pruning tools between each plant to avoid spreading disease. Regular deadheading to remove faded blooms promotes prolonged blooming and improves the appearance of the vines.