The bright mauve to purple flowers of Agathosma glabrata, commonly known as buchu, are an eye-catcher in any garden. Buchus are identified by the presence of small, round, oil glands present on the leaves and fruit. Crushing the leaves of this buchu releases a sweet lemon scent. Buchus are easily identified in the veld when brushing against a bush and smelling the sweet to pungent aroma.
Agathosma glabrata is slow growing and reaches a height of 0.5 to 1 m; it is an attractive, single-stemmed shrub with a round and dense habit and is bright and colourful when in flower. Masses of mauve, purple, white or pink flowers are borne in terminal clusters consisting of about 12 – 20 individual flowers. The flowering season starts in late winter until midsummer (July to December).
Leaves are tiny, dark green, and are 3 – 7 mm long. They are alternatively arranged on the side branches. Older branches are dark brown compared with younger branches which are cream-coloured to light green-brown, and covered with tiny white hairs, which are also visible on the reverse side of the leaves. The small oil glands which are scattered on the underside of the leaf, emit the sweet lemon scent.
The seed capsule is two-chambered with one shiny black seed in each chamber. As the seed capsule ripens or matures, it turns from pale l to dark green. The seed is scattered by ballistic dispersal or a catapult mechanism. If the seed capsule feels hard and not soft, it can be harvested.
Agathosma glabrata is threatened and has a Red-List status of Endangered (EN). According to Raimondo et al. (2009), there are only three known locations that continue to decline due to crop cultivation, urban expansion and alien plant invasion.
In 1984 a species thought to be glabrata was collected and propagated at Kirstenbosch NBG. It was written up in this series as aPlant of the Week by Norma Jodamus in 2006. In 2010, it was chosen as one of the species to be re-established to the Tokai Park in Tokai, Cape Town. Historic collecting records, however, showed that this species only occurs from Darling on the West Coast to the Cape Peninsula. The glabrata from Kirstenbosch had been collected on the Soetanysberg in the Agulhas National Park and could therefore not be considered for the restoration-project. Factors such as the possibility that this could be a totally different species, and if this was in fact the same species, it could belong to a another gene pool given the great distance between populations, were considered.
This meant the search for the real Agathosma glabrata was now on. Consultation of herbarium records and communication with people thought to have collected it for the last time more than twenty years ago, all proved to be fruitless. The possibility that this species had became extinct in the wild, seems likely. Then author (R.C. Oliver) received an invitation at the last minute to assist with a botanical survey of certain species along the West Coast recently. The species list for this survey, contained many rare and threatened species of the West Coast and was carefully perused. The list revealed the names of some exact localities, and with the friendly cooperation of the management at Jakkalsfontein Private Nature Reserve (near Yzerfontein on the west coast) , Kirstenbosch NBG and the Millennium Seed Bank Project, seed and cutting-material of A. glabrata were collected.
This species propagates easily and the Nature Reserve was keen when approached about the possiblility of re-introduction of material of this species into the wild. In the search of a suitable site, they also discovered a previously unknown population of this species on the Reserve. The species incorrectly identified as A. glabrata previously from Soetanysberg is regarded as either a natural hybrid or an entirely new species. Plants of the material collected from Jakkalsfontein have been re-established there and in Tokai.
Distribution and Habitat
There are about 150 species in the genus Agathosma and most of them are found in the Western Cape. Agathosma glabrata occurs naturally in damp sandy plains and dune slacks from Darling to the Cape Peninsula.
Derivation of name and horticultural aspects
Agathosma is derived from the Greek agathos meaning ‘pleasant', and osme meaning ‘smell'. This refers to the volatile oil in the glands on the leaves and fruit, and the word buchu is commonly used to describe indigenous small-leafed shrubs which release a pleasant to pungent aroma when touched. Each buchu species has its own unique scent. The Khoikhoi used the word buchu for an aromatic herb.
The species name glabrata means glabrous and refers to hairless leaves.
During the flowering season, masses of colourful flowers attract bees, butterflies and other insects which pollinate the flowers. Seed collected from fully ripened capsules show a higher germination percentage. If seed capsules are picked too early, the embryos are not developed and the seed will not be viable.
Uses and cultural aspects
Agathosma glabrata is an ideal garden plant cultivated for its aromatic leaves and beautiful flowers. Planted in masses or in groups of 3, 5 or 9 in small garden beds, it makes a colourful display. It can be used as a border or filler plant in a mixed fynbos bed with small to medium-sized plants. It can also be used as a pot- or container plant that will brighten up any patio.
Growing Agathosma glabrata
Buchus can be successfully grown from seed or cuttings. Fresh buchu seed is sown in autumn (March to April). The seed are is sown into a tray containing a well-drained medium of equal portions of sand, loam and compost. Use some of the medium to cover the seed and water. Place in a covered area with good light and air circulation. Keep medium wet to damp. Germination occurs in one to two months.
Young seedlings are pricked out into 0.5 l bags when four true leaves have developed, using a fynbos medium. Feed plants regularly but sparsely with a well-balanced fertilizer. Pinch out the growing tips of the seedlings to encourage bushy growth. Flowers are produced after two years.
After flowering, plants develop new shoots or branches, which are ideal for tip, stem or heel cuttings. The best time to make cuttings is in the summer (December – January) after flowering. Rooting is excellent and more than 80% of cuttings will root. Cuttings can also be taken during late autumn. Collect plant material early in the morning to reduce stress. Cuttings have the advantage of producing a larger flowering plant quicker than seedlings. Tip cuttings, 50 – 70 mm, are taken from the current year's growth. Prepare cuttings by making a clean cut below the node and remove a third of the foliage. Dip the base of the cutting in a rooting hormone such as Seradix 2. Firmly place the cuttings in a medium of 50% bark and 50% polystyrene and water cuttings with a fungicide. Ideally these cuttings should now be placed in an well-aerated propagation unit with a bottom heat of 24ºC. Rooting occurs in 9 to 11 weeks. Carefully pot the rooted cuttings using a well-drained, humus-rich fynbos potting medium (2 parts leaf mould, 1 part coarse sand). Plants will be ready for planting in seven to eight months, ideally during autumn to spring season. Feed regularly with a well-balanced nutrient. Yellow leaves can be treated with an application of iron chelate.
Agathosma glabrata as well as most of the species found in the Rutaceae family are best grown in the garden in full sun, in soil that is alkaline to acidic, well-drained and composted. Before planting, water the area and prepare the bed by digging over the soil, adding compost and a slow-release fertilizer. Plant out in groups of 3 to 5, 20 – 30 cm apart, with enough space to grow. It is a slow-growing plant and should not be planted too close to faster-growing plants. A layer of mulch is added after planting annually to keep soil and roots cool in summer, retain soil moisture and reduce weeds. Buchus are best planted out in autumn, winter and spring. Plants require good watering in winter and moderate watering in summer. Do not allow plants to dry out, and avoid cultivating the soil around the roots of these fynbos plants. They are water-wise plants and once established in your garden, they will survive long periods of drought and will withstand a fair amount of frost.
Agathosma glabrata is used as an accent plant, in a rockery, or in a mixed fynbos bed with companion plants such as Erica versicolor , Protea repens (sugarbush) , Leucospermum cordifolium (pincushion), Chondropetalum tectorum , Pelargonium cucullatum (tree pelargonium) and P. betulinum (camphor-scented pelargonium) and herbaceous perennials such as Lobelia valida , Geranium incanum and Scabiosa incisa . Interesting buchu species are Acmadenia heterophylla, Agathosma lanceolata (honey buchu), Adenandra uniflora (china flower), and Coleonema album (white confetti bush).
References and further reading
- Brown, N. & Duncan, G. 2006. Grow fynbos plants. Kirstenbosch Gardening Series. South African National Biodiversity Institute, Cape Town.
- Gold, M. 1992 . The buchus: cultivation and propagation . National Botanical Institute, Kirstenbosch.
- Goldblatt, P. & Manning, J. 2000 . Cape plants. A conspectus of the Cape flora of South Africa. Strelitzia 9. National Botanical Institute, Pretoria & Missouri Botanical Garden, Missouri.
- Stearn, W. 2002. Stearn's dictionary of plant names for gardeners. Timber Press, Portland, Oregon.