Flowering time (month)
Ornamental or utility value
moderately dry to fresh
weakly alkaline to weakly acidic
The black-eyed Susanne (Thunbergia alata) belongs to the genus of celestial flowers or Thunbergias and bears the botanical name “Thunbergia” in honour of the Swedish botanist Carl Peter Thunberg. The annual climbing plant, which originates from South East Africa, owes its German name to its eye-catching flowers, the dark centre of which resembles an eye. Black-eyed Susanne is one of the most popular climbing plants for greening garden fences, privacy screens and balconies. Susanne also cuts a fine figure as a traffic light plant or hanging from a wall projection.
Thunbergia alata is characterised by very rapid, luxuriant growth and striking, strongly coloured flowers. With a growth rate of up to 20 centimetres per week, it quickly winds its way up trellises, pergolas or very simple wooden rods up to two metres high. It should be noted that the growth direction of the shoots is always counterclockwise. Without climbing aid it becomes a beautiful hanging plant for balcony boxes, planters or hanging baskets.
The leaves of the black-eyed Susanne are slightly hairy, narrowly heart-shaped or triangular and sit on long, slightly winged stems. They reach a length of about seven centimeters and have a wavy edge.
From May to October the Susanne shows its three to four centimeter large white, yellow or orange flowers with black eyes. They are five-part and funnel-shaped. The dark eyes, however, are no longer typical for the black-eyed Susanne, because there are now also pure yellow, orange and white varieties. The climber is an extremely flowering plant: in warm and dry weather, the black-eyed Susanne appears as a large cascade of flowers.
Location and soil
Plant the black-eyed Susanne in a sunny, warm place, preferably sheltered from the wind. Cold, rain and wind are at the expense of the abundance of flowers. In wet, cool summers Thunbergia alata unfortunately often does not unfold its full splendour. Also a very windy location damages the flower formation. Loose and humus-rich soil is preferred. Use fresh, high-quality, permeable and nutrient-rich balcony potting soil for pot planting.
The rapid growth of the Thunbergie makes it an easy to grow climbing plant. The sowing of the black-eyed Susanne takes place between February and April at approx. 18 degrees Celsius in growing trays, preferably under glass. Germination only begins after two to three weeks. Then prick three plants into small pots and prune the tips to stimulate branching. At the end of May, after the ice saints, the plants can move to the open air or to the terrace. The first flowers appear about 15 weeks after sowing. It is also possible to sow the climbing plant directly outdoors in early summer. Since black-eyed Susanne needs up to four months for growth and flowering, this delays flowering until late summer.
Planting and care
So that the Climbing Axes can form strong roots, generous planters are advantageous on the terrace and balcony. Give the Thunbergie a stable trellis to hold on to right from the start and guide the tendrils upwards. Place the black-eyed Susanne in well-permeable potted plant soil and add some ripe compost or horn shavings. The very vigorous and therefore thirsty plant should always be kept moist and given a liquid fertilizer every two weeks for a splendid flower. However, waterlogging should be avoided at all costs! In the beginning the plants sometimes need some help climbing. Then you can loosely fasten the young shoots to the climbing aid with binding wire until the plant itself has found support. Lost shoots clinging to furniture or neighbouring plants are carefully loosened and twirled around the climbing aid. Disturbing or too long shoots can be cut without hesitation. Regular cleaning revives the flowering joy of the black-eyed Susanne.
Thunbergia alata is not winter-hardy and so the first frost in autumn unfortunately quickly brings an end to the flowering splendour of black-eyed Susanne. Although the plant is actually annual, it is possible to bring the Susanne into the house in a pot before the thermometer falls below the ten-degree mark at night, and to overwinter in a bright place at temperatures around ten degrees. During the winter months you should water less and not fertilize. In February the plant is strongly pruned back. But because Thunbergia alata is easy to sow and extremely fast-growing, it is usually not worth spending the winter. In addition, the joy of flowering often decreases considerably in the second year.
The black-eyed Susanne is often used as a climbing or hanging plant on the balcony or terrace. But also on obelisks in flower beds, garden fences or trellises, it winds its way nimbly along and forms a blossom-rich screen greening. In order to achieve a dense flower curtain, you should plant several plants per climbing aid at the same time. Red and blue flowering plants such as sage are ideal companions.
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Various blends are available on the market, for example ‘Blushing Susie’ with flowers in cream colours and apricot to red. Beauty Spots’ is a mixture of white, cream and yellow flowers. African Sunset’ shines in a colour gradient from apricot to pink to cream white. The ‘Superstar Orange’ variety is the largest of the classic orange Susannas. Thunbergia alata ‘Salmon Shades’ bears bright salmon-coloured flowers in various colour intensities.
The black-eyed Susanne is most easily propagated by sowing in spring. In late summer it is also possible to cut head cuttings from well-ripened shoots, remove the lower leaves and root them in a sanded, well-permeable cultivar. The young plants are then planted out after wintering next May.
Diseases and pests
If the black-eyed Susanne stands too wet, it can come to root rot. Signs of this are pale green, wilted leaves and persistent wet substrate. In this condition the plant is unfortunately often no longer salvageable and must be disposed of. Susanne is particularly susceptible to spider mites, white flies and scale insects in winter quarters and should be checked regularly for infestation.
Whether potted plants such as oleanders or indoor plants such as orchids: The scale insect infests the most diverse plants. René Wadas, a herbalist, will give you his tips on pest prevention and control: Production: Folkert Siemens; Camera: Fabian Primsch; Editing: Dennis Fuhro; Photo: Flora Press/Thomas Lohrer
I am Don Burke, one of the authors at My Garden Guide. I am a horticulturist that cultivates, grows, and cares for plants, ranging from shrubs and fruits to flowers. I do it in my own garden and in my nursery. I show you how to take care of your garden and how to perform garden landscaping in an easy way, step by step.I am originally from Sydney and I wrote in local magazines. Later on, I have decided, more than two decades ago, to create my own blog. My area of specialization is related to orchid care, succulent care, and the study of the substrate and the soil. Therefore, you will see many articles dedicated to these disciplines. I also provide advice about how to improve the landscape design of your garden.