Diascia, sometimes called twinspur, is one genus of approximately 70 species of the Scrophulariaceae family, a perennial plant that is native to the southern regions of Africa. Prior to 1985, diascia was not commonly cultivated outside of its native habitat but has gradually become an increasingly popular flowering plant on a worldwide level. The late Hector Harrison of Appleby, North Lincolnshire, England, bred many different hybrids of diascia, resulting in several cultivars that have been selected and named. The plant is suitable for use in hanging baskets, window boxes and as bedding plants. Harrison increased the color range to produce blossoms of white, pink, red, coral, apricot, pink and lilac.
Twinspur references the two spurs located on the back side of the flower, usually pointing down. The spurs contain oil that is collected by bees of the rediviva species. This bee has especially long forelegs in order to collect the oil and is believed to have co-evolved with the plants.
Most species of diascia are straggling plants that reach no more than about 12 to 18 inches (30 to 45 cm) in height. Some diascias produce several lax stems from one crown, and others spread by means of stolons. The corolla usually is rose colored or pink in the perennial species that is most commonly cultivated, with five lobes. Patches of oil glands appear to be dark purple and might make the flowers of some species look dual in color. The flowers are germinated in loose terminal racemes.
Often treated as an annual, diascia actually is a short-lived perennial. In many places, these plants typically bloom through several light frosts until late autumn. The plants should be taken inside into an unheated but above-freezing environment in the winter. They will go semi-dormant through the winter months and return to flowering in the spring. They also can be treated as annuals and discarded.
Most diascia start from cuttings, because seeds for the plant are not often sold. If seeds can be found, the best time for sowing is six to eight weeks before the last frost. Diascia needs light to germinate, so the seeds should be pressed lightly into sterile potting soil. The soil should be kept moist, and germination should occur in about three weeks.
Diascia does require some light fertilization, especially if placed in containers and baskets. Too much fertilization produces more foliage than flowers, so a low-nitrogen fertilizer should be used with moderation. The plants should be kept moist but should not be over-watered. Cutting the plants back if they get lanky encourages fuller plants with more flowers.