Agathosma capensis is a variable shrub with either hairy or glabrous (hairless) leaves. Flower colour ranges from mauve, pink to white or a bluish purple. Crushed leaves emit a sweet, spicy scent. The common characteristic of the Rutaceae (buchu) family is the presence of translucent cavities (glands) containing aromatic oils found on the leaves or fruit.
Agathosma capensis is an evergreen shrub, 300-900 mm high. Grown among taller vegetation, it can reach a height of 1.5 m. It forms a single stem at the base and grows into a small, rounded bush. The branchlets are glabrous (hairless) or pubescent (covered with fine hairs). The older stems are woody, whereas the younger stems are softer and covered with small, aromatic leaves. The green leaves are linear, 1.5-7.0 mm long, obtuse or rounded at the apex (leaf tip) and alternately arranged on the branches. The inflorescence is borne at the tips of branches or on the lower axillary, the angle between the leaf and the branch. Flowers are crowded in flat-topped clusters or rounded heads, are 5-petalled and 3-5 mm long, with noticeable stamens. Petals have a distinct claw and flower stalks are 5-10 mm long. Flowers are present throughout the year with a peak in July to November. The fruit capsule consists of 2 or 3 chambers; each chamber contains one black seed. The seed ripens in November to December.
Agathosma capensis is not listed as a threatened species on the Interim Red Data List.
Distribution and habitat
Agathosma capensis is widely distributed. It grows in soils derived from mineral-rich rocks, on granite, shale or coastal sands on mountain slopes and flats from Nieuwoudtville, Port Elizabeth to Grahamstown. It is seldom found growing on acid sand. This species has been collected at an altitude of 15 to 1 800 m.
Derivation of name and historical aspects
The genus name Agathosma (Willd.) is derived from the Greek agathos, meaning pleasant and osme, meaning smell or scent. The oil glands on the leaves and fruit release a sweet to strong fragrance when crushed. The species name capensis in Latin means of the Cape or from the Cape Colony, or of the Cape of Good Hope, South Africa. Agathosma capensis belongs to the Rutaceae, commonly known as the citrus family.
In the genus Agathosma there are 150 species of evergreen shrubs, varying in height, with flowers usually white, pink or purple. They occur mainly in the Western Cape.
Agathosma was previously known as Barosma.
Other interesting species : Agathosma glabrata is an attractive single-stemmed shrub with bright mauve to purple flowers in autumn. A. lanceolata grows up to 500 mm high; the crushed leaves release a liquorice/honey scent; it is best displayed along borders. A. mucronulata forms a neat, compact shrub, 0.8-1.0 m tall. Masses of white flowers are produced during autumn to spring.
After fire, Agathosma capensis resprouts from its persistent rootstock. Seeds are collected and stored by ants away from rodents, and germinate and grow after good rains.
Uses and cultural aspects
Agathosma capensis is an attractive small buchu with great horticultural potential and is not often used in gardens. It is best used as a border plant by planting masses; or as a pot plant. It is ideal for the water-wise garden or fynbos garden.
Growing Agathosma capensis
Agathosma capensis is a small to medium shrub and best used as a border plant in a mixed fynbos garden. It grows well in gardens with full sun and well-drained soil. Before planting, prepare the garden bed by digging over the soil, adding compost and a slow-release fertilizer. Plant during autumn, winter and spring with a combination of pelargoniums, proteas, aloes, restios, watsonias, Leucadendron and other interesting companion plants. Water the garden area before planting. Plant out in groups of three or five, 20-30 cm apart, with enough space to encourage growth. Buchus respond to a fairly dense planting which helps to retain soil moisture. 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. Plants can be maintained in the garden for several years by pruning, once the bush becomes untidy.
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 slow-growing plants and should not be planted too close to faster growing plants. Add a layer of mulch after planting and annually to keep soil and roots cool in summer. It retains soil moisture and reduces weed seed from germination.
Agathosma capensis germinates from seed and is sown in autumn. Sow seeds on a prepared medium of sand and compost in equal parts in a seed tray. Cover seeds with a thin layer of bark and water. Place seed trays in a covered area with good light and ventilation. Keep seed trays damp and germination will take place within one to two months. Prick out seedlings when four true leaves have developed. Take care not to damage the fine roots. Harden off seedlings under shade for 3-4 weeks before placing in the sun. Pinch out the growing tips of seedlings to encourage bushy growth. Feed buchus regularly with a balanced nutrient. The yellowing of leaves can be treated with an application of iron chelate. After 8 to 9 months the plants can be planted out in the garden.
Propagate by rooting heel, tip or semi-hardwood cuttings. Take fresh cuttings from the current year's growth. Cuttings have the advantage of producing a larger flowering plant more rapidly than seedlings. Prepare cuttings by making a clean cut below the node and remove a third of the foliage. Dip the base of the cuttings in a rooting hormone. Firmly place the cuttings in multi-trays filled with a medium of 50 % bark and 50 % polystyrene. Place cuttings in a well-aerated propagation unit under mist with heated benches. Rooting occurs in 9-11 weeks.
Pot rooted cuttings, using a well-drained, humus-rich fynbos potting medium (2 parts leaf mould and 1 part coarse sand). Keep plants under shade for three weeks to harden off before placing them in the sun. Plants will be ready for planting in 7-8 months.
Pinch back young buchu plants to encourage bushy growth. Once established, do not cultivate the soil around the root area.
Phytophtera cinnamonnii, a soil and water-borne fungus, attacks the roots of most fynbos species. High soil temperatures promote the growth of this fungus, attacking the plant's root system. It prevents the uptake of water, causing plants to die. Remove infected plants and use soil mulch to reduce the soil temperature. Disturb the soil as little as possible. Treat plants with a fungicide prior to planting out. This is a precautionary measure to control the fungus and to protect adjacent plants.
References and further reading
- Gold, M. 1992. The buchus : cultivation and propagation. National Botanical Institute, Cape Town.
- Goldblatt, P. & Mannning, J. 2000. Cape plants. A conspectus of the Cape flora of South Africa. Strelitzia 9. National Botanical Institute, Pretoria & Missouri Botanical Garden, Missouri.
- Le Roux, A. 2005. Namaqualand. South African Wild Flower Guide 1, edn 3. Botanical Society of South Africa, Cape Town.
- Manning, J. & Goldbladtt, P. 1997. Nieuwoudtville, Bokkeveld Plateau and Hantam. South African Wild Flower Guide 9. Botanical Society of South Africa, Cape Town.
- Mason, H. 1972. Western Cape Sandveld flowers. Struik, Cape Town.
- Moriarty, A. 1997. Outeniqua, Tsitsikamma and eastern Little Karoo. South African Wild Flower Guide 2. Botanical Society of South Africa, Cape Town.
- Stearn, W. 2002. Stearn's dictionary of plant names for gardeners. Timber Press, Portland, Oregon.
- Van Rooyen, G. & Steyn, H. 1999. Cederberg, Clanwilliam and Biedouw Valley. South African Wild Flower Guide 10. Botanical Society of South Africa, Cape Town.