African hemp, also called Cape stock rose, Cape hollyhock, House Lime and African linden, is native to South Africa. Its botanical name is Sparmannia africana after the Swedish botanist Dr Anders Sparmann who travelled with Captain Cook on his second voyage, but came across this plant on a separate expedition to South Africa in around 1796.
In its native country, African hemp can reach four metres high although around two metres is more usual. The large leaves are a typical lime tree shape (Tilia, not the citrus lime, hence the common names House lime and African linden - linden is another name for a lime tree). They are apple-green and covered with soft, fine hairs.
African hemp produces lots of white flowers approximately 3.5cm across in late winter or early spring. In the centre of each flower is a powder-puff of red and yellow stamens. These stamens are haptonastic, meaning that they move quickly in response to stimuli. The movement is almost instantaneous and is believed to assist pollination. Another example of haptonasty in plants, and one which many gardeners will be familiar with, is the 'Touch-me-not' plant which closes up its leaves when touched.
In the wild, African hemp grows on the edge of forests so it is best placed in a position where it will get partial shade in the summer. It needs a rich soil and will benefit from a fortnightly feed as soon as the first buds appear.
It is not frost resistant and will need protection during the winter; in very cold inland areas it would probably be advisable to bring it indoors onto a bright windowsill. African hemp can be pruned after flowering to keep it compact.
Propagation is by tip cuttings which should root easily in water.
There is a variegated form, S. Africana variegata and a double flowered variety called S. Africana flore-pleno.