A special delight for the summer garden is Wahlenbergia undulata with its soft mauve bells dancing on long slender stems. This giant bellflower grows wild throughout the summer rainfall areas of southern Africa. It is quite commonly found in the grassland, usually in rocky or seasonally moist places.

A soft perennial or annual, Wahlenbergia undulata in full flower forms cushions of about 60 cm high. From the base of the plant the woody older stems fork repeatedly, growing softer and greener towards the flower-bearing tips. The narrow, simple-shaped leaves are stalkless and grow on the bottom half of the stems. They vary in size. The form at Kirstenbosch has leaves measuring about 3 cm long and 1 cm wide. The leaf margins or edges are always wavy. This simple feature can help to differentiate between Wahlenbergia undulata and other similar looking species. Tiny white hairs are scattered along the stems and leaves.

The colour of the flowers can vary from bluish-mauve to very pale blue or even white. Flowering is from mid to late summer, with each flower lasting a few days and every plant flowering for more than a month. The long flower stalks often droop at the top while the flowers are still in bud, but straighten as the flowers open. The bell-shaped flowers are formed by 5 petals that are pointed at the tips and join together halfway down. Many little veins run through the soft petals with one much darker line along the middle of each petal. This dark mauve line runs from the tip of the petal down to the centre of the flower where the nectar glands are found. The line probably serves to guide pollinators such as bees. The style and stigma are prominent in the centre of the flower. In the young flowers, the pollen is released before the stigma opens and sticks to the pollen collecting hairs on the style. In the older flowers, the stigma unfolds, opening wide to present three pure white lobes. The flowers measure about 5 cm across, but flowers from different localities in the wild can vary in size. Once the petals have wilted, the 5 long pointed tips of the calyx remain looking like little stars around the ripening seed capsules. Within a few weeks after flowering, the seed is ready and thousands of little seeds are released through 3 pores, which open at the top of the seed capsule.

Growing Wahlenbergia undulata

In the garden it is best to display Wahlenbergia undulata in a rockery or raised bed, where the plants can form soft hanging cushions and can be viewed close-up. They grow in full sun to semi-shade, in ordinary good garden soil. The plants require good drainage with regular watering in summer. New plants should be planted out from spring to early summer, to give the plants enough time to establish themselves and grow bushy before flowering in mid-summer. At the end of summer after flowering and seed collection, the untidy dead stems need to be cut back. During winter the plants go dormant and look almost dead, before new growth shoots in spring. Plants live for 2 - 3 years before dying off.

Plants can be propagated from cuttings or seed. Seed is usually faster, easier and more reliable. The fine seeds can be sown in autumn or spring. Sow the seeds in a seed tray filled with a well-drained medium and cover lightly with a layer of white sand or finely milled bark. Place the tray in a protected shade area and water regularly. Germination is usually good and within 2 - 3 weeks. The seedlings are sometimes slow to grow, but feed them with an organic fertilizer and plant into individual containers as soon as they are big enough to handle. Unfortunately, the plants do not look good in containers for long and should be planted out into the garden as soon as the roots are strong and the plants actively growing. The plants do not display well in containers and this may be the reason why they are so seldom sold in nurseries.

Wahlenbergia rivularis

Wahlenbergia rivularis is another perennial wahlenbergia at Kirstenbosch. It flowers throughout the summer with beautiful white to cream bells. It prefers a slightly more damp soil than Wahlenbergia undulata and grows in full sun or semi-shade. The growth habit also differs from that of Wahlenbergia undulata. It spreads along the ground forming a groundcover of soft green leaves with white flowers about 30 cm above the ground. Wahlenbergia rivularis looks lovely planted along the edge of a path or a pond. It goes slightly dormant in winter looking a bit untidy, but remains green. Wahlenbergia rivularis roots as it spread making it easy to propagate by division, from cuttings or seed.

There are about 267 species of Wahlenbergia worldwide, of which most are found in South Africa. Most of them are annuals or herbaceous perennials with bell-shaped flowers in shades of mauve, blue, white, or cream.