Diascia are a pretty group of perennial herbs often with soft coral-pink or bright pink or white flowers with two spurs from S. Africa, allied to Alonsoa, snapdragons and nemesia. The flower is shaped with a large drooping lower lip, being related to the Snapdragon family, but have two spurs on the lower lips like nemesias and four smaller curly petals at the top, a throat to each flower sort of like a penstemon. The flowers are tubular like foxgloves and are arranged in clustered racemes.
Diascias are nicknamed Twinspurs because the have two ‘spurs’ (in Greek – di – ascia meaning di = two and askos = sac), referring to the two oil containing spurs at the back of their flowers.
The pollination of diascias by special oil collecting bees in the wild, is fascinating. These specialized bees have modified forelegs with which they collect oil from inside the two spurs. Once cross-pollinated, little round seeds are formed in capsules. Within a few weeks the seed capsules turn brown and dry, split open and release the ripe seeds that are black and hard.
The genus Diascia contains about 70 species, and is found only in southern Africa (Drakensburg mountains in Lesotho, Western Cape and Namaqualand). Diascia VARIETIES include: D. rigescens; D. vigilis; D. barberae though in the early part of the last century most British gardening encyclopedias listed just one diascia – Diascia barberae – derived from seed collected by Col J.H.Bowker and sent by a Mrs Barber to Kew in 1870. Annual and perennial diascias had, of course, already been discovered and classified by several botanists visiting South Africa much earlier. The perennial species were soon discovered to be half hardy in most of Europe and drew little horticultural attention. A reviewer for Curtis’ Botanical Magazine in 1871 mentioned them, but seemed to have a mixed opinion of them describing Diascia barberae as a member of the ‘pretty Cape genus Diascia’ but going on to comment that ‘most of them (diascias) are inconspicuous – flowered plants and little worthy of cultivation for their beauty’. Only recently have these flowers become very popular.
They are found wild in South Africa, the Drakensberg mountains and West Lesotho. They are loved for its fantastic flowering ability. Flowers smother the plant for months over the summer. They are also good for providing spring color in the garden and thrive as rockery plants, and are considered among the most beautiful of trailing patio container or border plants. Diascia flowers in cycles, which means that you get blooms in flushes. The flowers respond to warmer temperatures included increased growth and flowering.
If raised in heat in spring and planted out in May, it flowers until late autumn and here in Japan through the winter too, they flower best if kept small by pinching and deadheading. Often treated as a half-hardy annual, the roots are perennial in the warm soils of southern gardens, spreading by stolons into handsome tufts.
- STEP 1: Buy healthy, green plants with no signs of wilting or disease. Plants should be stocky, with plenty of leaves. It’s actually a plus if they don’t have any flowers on them – they’ll divert their early energy into root development rather than flowering.
- STEP 2: Choose a site. Twinspur likes full sun, but appreciates light shade in warmer parts of the country. It also needs excellent drainage and won’t thrive in wet, clay soil. Sandy soils, raised beds, slopes, rock gardens and containers are all better bets.
- STEP 3: Start seed indoors 6-8 weeks before last frost or in spring after frost has passed. Cover seed lightly and provide average temperatures; 18-21°C (65-70°F). Should germinate in 7-14 days. May be direct seeded in early to mid-spring after all risk of frost. Transplant outside after last frost into a full sun or part shade location, 6-12″ apart. Diascias like lots of sun, but in hot-summer areas some shade will help keep them blooming. They are said to like a cool root zone, so much like a clematis, their roots should be shaded from hot blazing sun. Prefers well-drained, rich alkaline soil that is not too dry. NO STANDING PUDDLES TOLERATED.
- Pinch tips of young plants. Cut back if flowering slows down.
- STEP 4: Keep soil evenly moist. Mulching is a good idea.
- STEP 5: After the first flowers have faded, cut the plants back to just 2 inches high to rejuvenate them and encourage a new flush of bloom.
- STEP 6: Fertilize every four to six weeks, or work in a slow-release fertilizer (or plenty of compost) at planting time.
- STEP 7: Tear out and discard plants after heat arrives and plants become ratty-looking.
— December 21, 2006