Sparrmannia africana aka African Hemp

Sparrmannia africana is generally considered easy to grow as a large container or conservatory plant. It is a vigorous evergreen that responds well to bright dappled light, free-draining loam-based compost and consistent watering, and it propagates readily from seed or semi-hardwood cuttings. The main pitfalls are overwatering, which causes rapid leaf rot, and exposure to frost, since the plant cannot tolerate temperatures below about 7 C.

This is a large, vigorous evergreen shrub that ultimately reaches about 4-8 metres tall and 2.5-4 metres wide, taking 10-20 years to attain its final size. Indoors and in containers it is typically kept much smaller through annual pruning, which also encourages a bushy habit and more flowers. Growth is moderate and the soft-wooded stems can be cut back hard if the plant outgrows its space.

Sparrmannia africana is native to the southern coast of South Africa, ranging from Riversdale in the Western Cape east to Port Elizabeth in the Eastern Cape, where it grows on damp forest margins, hill slopes, ravines and along streams. Some references additionally cite Madagascar as part of its natural range. It is now widely cultivated as a houseplant and conservatory subject in temperate Europe and other parts of the world.

Water Sparrmannia africana well, particularly in spring and summer when it is actively growing, but always allow excess water to drain away. The species comes from damp forest-margin habitats so it appreciates consistent moisture, but it dislikes waterlogging - excessive watering causes rapid leaf and root rot. Reduce watering noticeably in winter when growth slows.

Use a fertile, loam-based potting mix high in organic matter and with sharp drainage. The species is unfussy about soil pH, tolerating acid, neutral or alkaline conditions, and grows on chalk, clay, loam or sandy substrates in the wild and in gardens. A topdressing of compost or organic mulch each year keeps it vigorous.

Provide bright but filtered light - dappled sun, partial shade or a few hours of direct morning or late-afternoon sun (around 2-6 hours total). Indoors, an east- or south-facing window or a sheltered conservatory position works well. Deep shade reduces flowering, while harsh midday sun can scorch the soft, pale leaves.

Sparrmannia africana is tender and rated RHS H1c, meaning it tolerates roughly 5-10 C as a minimum and needs heated greenhouse or indoor conditions in winter; it cannot survive frost or temperatures below about 7 C (45 F). Keep it in a sheltered spot away from cold draughts and avoid exposed, windy positions outdoors. Normal indoor room temperatures suit it year-round.

Treat the plant generously during the spring-to-summer growing season with steady watering and active feeding, then ease back on water in autumn and winter as growth slows. Prune annually after the main flush of flowers - which runs from late winter through early summer - to maintain a bushy shape and encourage new flowering wood. In cool climates move container plants under glass before the first frost.

Sparrmannia africana produces clusters of crisp white flowers about 3.5 cm across, each with a striking central tuft of yellow and red-purple stamens, borne in showy 10-20-flowered cymes. They appear from mid-winter into early summer in the native range and through spring and summer in the Northern Hemisphere. The petals are reflexed - swept back - which helps direct rainwater away from the reproductive parts of the flower.

The straight species Sparrmannia africana is the form usually grown, and it has received the Royal Horticultural Society's Award of Garden Merit. A double-flowered form, sometimes sold as 'Flore Pleno' or 'Plena', is occasionally available, and other Sparrmannia species exist within the small genus, which contains up to seven species in total.

Outdoor cultivation is only practical in essentially frost-free climates, since the plant cannot tolerate temperatures much below 7 C. In the UK and similar temperate areas it is grown under glass or in a sheltered courtyard against an east- or south-facing wall, and brought inside for winter. In warmer regions such as parts of California, the Mediterranean and southern Africa it can be grown as a fast-establishing garden shrub.

Prune Sparrmannia africana annually, ideally after the main flowering flush, to keep it bushy, control its considerable size and encourage new flowering shoots. The wood is soft and easy to cut, and the plant tolerates fairly hard pruning. Pinching tips on younger plants also helps produce a denser specimen.

The species propagates easily, both from seed sown in spring or summer and from semi-hardwood cuttings taken at the same time of year. Cuttings root readily in a free-draining cutting compost; rooting hormone is helpful but not essential. Seedlings and rooted cuttings grow vigorously once established.

The large, soft, hairy leaves accumulate dust readily, so wipe or rinse them periodically and provide good air circulation around the plant. Adequate airflow is also important horticulturally, because still, humid conditions encourage fungal leaf problems on this species.

Yellowing leaves are most often a sign of drought stress; the plant has a high transpiration rate through its big, soft leaves and wilts and yellows quickly when the rootball dries out. Persistent yellowing combined with soggy compost, on the other hand, points to overwatering and incipient root rot, since waterlogging is the other main cause of leaf decline.

Brown leaf edges and patches typically follow either prolonged drought or fungal leaf spotting in stagnant, humid conditions. Improving air circulation around the plant, watering more consistently and removing affected leaves usually resolves the issue. Cold draughts and frost damage can also brown the foliage on plants kept too cool.

Drooping leaves on Sparrmannia africana almost always indicate water stress - either a dry rootball, in which case a thorough soaking quickly revives the plant, or root rot from waterlogged soil, which requires repotting into fresh, free-draining compost. Cold damage in winter can also cause limp, drooping foliage.

Leaf drop is a common reaction to environmental stress in this species: cold draughts, sudden temperature changes, prolonged drought or overwatering will all trigger shedding of older leaves. Once conditions are corrected the plant typically flushes new growth quickly, given its naturally vigorous habit.

Slow growth is unusual for Sparrmannia africana, which is normally vigorous; when it occurs it usually reflects insufficient light, root-bound containers, depleted compost or cool temperatures. Repotting into fresh loam-based compost, providing brighter dappled light and warmer conditions, and feeding during the growing season generally restores its typical vigour.

Under glass and indoors the most common pests are glasshouse whitefly and red spider mite, both of which thrive in warm, dry conditions; regular misting, good airflow and prompt treatment keep them in check. The species is generally disease-free, but poor air circulation can lead to fungal leaf spotting.

Sparrmannia africana is insect-pollinated, with bees as the main visitors in its native habitat. Its flowers display a striking adaptation called haptonasty: when a stamen is touched, the surrounding cluster of stamens springs outward in a small puff, dusting the visiting insect with pollen and improving cross-pollination. The reflexed petals also help by keeping rainwater away from the reproductive parts.

The species has been used traditionally as a medicinal plant in southern Africa, and Kew's Plants of the World Online records it as having medicinal applications. Specific preparations and uses are not well documented in modern reputable sources, however, and there is no evidence-based clinical data supporting any particular medicinal claim.

Beyond ornamental and houseplant use - which is the dominant role of Sparrmannia africana, particularly in Europe where it became popular in the 19th century - the species has very limited additional uses. Historical attempts to commercialise the bark as a hemp-like fibre, which gave the plant its common name 'African hemp', were ultimately unsuccessful. Kew also lists general environmental uses for the species.