The mildly aromatic Agathosma collina is a hardy shrublet suitable for strandveld or coastal areas where it will cheer up the garden with its bright yellow-green leaves.
Agathosma collina is a dense dwarf shrub that grows to a height of 0.3–1 m and has a width of 1 m. The oval leaves, which are between 3. 5 and 5 mm long, are tipped with a rigid hair. This rounded and single-stemmed shrublet has dense clusters of white flowers with petals 4.5 mm long. The flowering period is from October to April.
||Left: Agathosma collina flower head
Right: Agathosma collina flowering buds
Agathosma collina has a status of Near Threatened (NT) (Raimondo et al. (2009). There has been a decline of this species outside the De Hoop Nature Reserve due to coastal development and invasion by alien plants.
Distribution and habitat
The distribution of this buchu is restricted to the coastal dunes and limestone hills from Agulhas to Still Bay in the Western Cape.
Derivation of name and historical aspects
The genus name Agathosma is derived from Greek agathos, which means good, and osme which refers to fragrance. This is meant to indicate the distinctive fragrance so closely associatedwith the genus. The oil glands present on the leaves and fruit normally release an aromatic fragrance when crushed.
The specific epithet, collina, pertains to hills. This refers undoubtedly to the limestone hills of its natural habitat.
There are 150 Agathosma species of which most are confined to the Western Cape.
Plants of this species are virtually immune from attack by insects. This is due to the leaf glands which secrete an aromatic and often pungent smell.
During the flowering season, bees can regularly be observed visiting plants.
Uses and cultural aspects
Buchus seem to become ever more popular and it is not just the relatively common Agathosma betulina and A. crenulata which are primarily grown for their medicinal value.
Buchus have huge potential as ornamentals and that, coupled with their water-wise nature, should make them highly desireable for many a garden. Some rather well known buchus in the landscaping industry include: Agathosma ovata “Kluitjieskraal', A. serpyllacea, Coleonema album and C. pulchellum. Agathosma collina makes an excellent garden subject here at Kirstenbosch NBG and really belongs to this latter category. The dwarfed form of this species perhaps lends itself to growing in pots.
Growing Agathosma collina
Sow the seed of Agathosma collina in autumn on a medium consisting of equal parts sand and compost in a seed tray. River sand will also suffice as a medium. Cover seeds with a thin layer of bark and then water. Now the seed trays should be placed in a covered area with plenty good light and ventilation. Ensure trays do not dry out or get overwatered. Germination will take place within one to two months. Seedlings are ready for pricking out when four true leaves have developed. Take care not to damage the fine roots. Harden off the seedlings by placing them in shade for 3–4 weeks before placing them in the sun. It is ideal to pinch out the growing tips of seedlings as this will encourage a bushy growth. Buchus can be regularly fed with balanced nutrient products such as Kelpak and later Seagrow. After 8 to 9 months plants should be ready for transplanting in the garden.
Vegetative propagation is done by heel, tip or semi-hardwood cuttings. Fresh cuttings should be taken from the current year's growth. Prepare cuttings by making a clean cut below the node and remove a half to a third of the foliage. The base of the cuttings is dipped in a rooting hormone and then placed in trays filled with a medium consisting of one half bark and one half polystyrene. Place cuttings in a mist-unit with heated benches which will speed up the rooting. Rooting occurs in 9–11 weeks. Rooted cuttings are moved to harden off for 2–3 weeks.
The rooted cuttings are potted in a well-drained mix and than moved to a shady area for 2–4 weeks where they can harden off. After this period, they can be moved to full sun. These young plants will be ready for planting in the next 7– 8 months.
Agathosma collina will do well in gardens with full sun and well-drained soil where it is planted amongst other fynbos species. The best time for planting is between autumn and winter. The rainy season allows buchus to establish themselves in the garden and to cope with drought and less water during summer. Once established, they will withstand a fair amount of frost. Before any planting commences though, it is advisable that the garden bed is prepared by digging over the soil, adding well-rotted compost and a slow-release fertilizer. Companion plants can include: Leucospermum patersonii, L. truncatum, Protea obtusifolia, Leucadendron meridianum, L. muirii, Ficinia truncata, Chondropetalum microcarpum, Thamnochortus fraternus, T. pellucidus, Ischyrolepis eleocharis, Helichrysum dasyanthum, Pelargonium betulinum, Salvia africana-lutea, Erica spectabilis, E. regia subsp. mariae, Delosperma litorale, Lampranthus amabilis, Jordaaniella dubia, Lobelia valida, Satyrium carneum and Haemanthus sanguineus. Suitable buchu species include: Agathosma riversdalensis, A. dielsiana, A. serpyllacea, Acmadenia obtusata, A. mundiana, Adenandra gummifera, Diosma guthriei, D. haelkraalensis and Euchaetis meridionalis. Plant at 20–30 cm intervals, which should provide enough space to encourage growth.
Buchus prefer a rather dense planting as this helps to retain soil moisture. Plants require a good watering in winter and only moderate watering in summer. Plants must never be allowed to dry out completely. Regularly add a layer of mulch to help keep soil and roots cool in summer.
Plants can be maintained in the garden for several years by pruning, once the bush becomes untidy.
References and further reading
- 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.
- Gould, M. 1992. The buchus: cultivation and propagation. National Botanical Institute, Cape Town.
- Powrie, F. 1998. Grow South Africanplants. A gardener's companion to indigenous plants. National Botanical Institute, Cape Town.
- Mustart, P., Cowling, R. & Albertyn, J. 1997. Southern Overberg. South African Wild Flower Guide 8, edn 1. Botanical Society of South Africa, Cape Town.
- Raimondo, D., Von Staden, L., Foden, W., Victor, J.E., Helme, N.A., Turner, R.C., Kamundi, D.A. & Manyama, P.A. (eds) 2009. Red List of South African plants. Strelitzia 25. South African National Biodiversity Institute, Pretoria.
- Stearn, W. 2002. Stearn's dictionary of plant names for gardeners. Timber Press, Portland, Oregon.
Roger Oliver & Tamzin Lakey
Kirstenbosch National Botanical Garden