Thunbergia : Greenhouse Plants
FF – frost free only / C – cool, minimum of 7°C (45°F) / W – warm, minimum of 13°C (55°F) / T – tropical, minimum of 18°C (65°F)
Thunbergia alata from South Africa, referred to as Black Eyed Susan, is probably the species most people will identify with although there are many more worthy of greenhouse cultivation. There are different forms of T. alata so that white, yellow or orange flowers can be grown. As it is easy to grow them as an annual for use outside it is best not to waste greenhouse space on them. T. grandiflora from Northern India makes a very tall climber producing beautiful blue flowers in summer. There is also a white form. T. laurifolia from Malaya is very similar and, fortunately, both species will flower as small plants and grow well in a warm house. T. fragrans is a moderately sized white flowered climber from India which in actual fact is not fragrant at all. Unfortunately, when a flowering shoot was sent to England to be identified and named it was packed in a box which had previously contained scented soap and the flowers appeared to be heavily perfumed by the time they were unpacked and named.
This plant likes tropical conditions as does the extremely showy T. mysorensis from India which is another climber with long pendant racemes of brilliant yellow flowers with purple throats.
As all these plants climb to a good size they will become straggly and in need of pruning after they have flowered. If it is necessary to restrict their size they can be cut down to within a few buds of thesurface if the wood is quite young in which case the whole plant will be regenerated. However, for really good flowering a structure of older shoots should be trained up a support and lateral shoots produced from these can be cut back close to the older wood annually.
T. natalensis is a useful shrubby plant that is virtually hardy. It is certainly suitable for a frost free house and can be treated as a herbaceous perennial. Shootshould root easily in a propagator at 15-24°C (60-75°F). Seed should be just covered and given 21-24°C (70-75°F) to germinate.