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.
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.
Liesl van der Walt