How to Grow and Care for African Hemp
The Sparmannia is a member of the Tiliaceae or Lime family, of which there are some four known species. They are all natives of South Africa, where they grow into quite sizeable shrubs, on average about 12 ft (4 m) high.
The plant was named after Dr. Anders Sparmann, a Swede who lived from 1748 to 1820 and accompanied Captain James Cook on his second voyage. Its common names are African hemp and room or house lime. Only one variety, Sparmannia africana, is commonly grown (particularly in parts of Europe) as a houseplant.
The plant grows rapidly in a pot in the home to 3–4 ft (90–120 cm) but requires a well-lit position. The leaves, which resemble those of the outdoor lime in shape, are covered with soft hairs that make them a little difficult to clean. Very dusty plants can be cleaned in summer by standing them out in light rain.
When African hemp is mature and 3 ft (1 m) or more in height, it will bear clusters of white fragrant flowers, each centered with a powder-puff of red and yellow stamens, most often in late winter to early spring. Large plants are a bushy shape and are best grown alone so that air can circulate freely around them.
When buying in the spring or early summer, look for bright coloring in the lime-green leaves with no yellowing of the lower leaves. Also make sure that no branches are broken, since the new growth is very soft and can easily be damaged on its journey from the nursery to the shop.
Proper Care Guide
Atmosphere: African hemp are fairly tolerant but do not like draughts, which can produce leaf drop. They appreciate some ventilation in summer.
Cleaning: A feather duster lightly flicked over the leaves will remove dust, or you can brush them gently with a soft, dry paintbrush. Never add water or leaf shine. In summer, stand the plant outside in light rain to wash the dust off its leaves.
Feeding: Apply standard liquid fertilizer once every 2 weeks from spring (or earlier, if flower buds appear before that) to autumn.
Humidity: Mist-spray during the summer 2 or 3 times a week.
How to Take Stem Tip Cuttings
Light: Sparmannia africanas must have plenty of bright filtered light, otherwise the leaves will go yellow, and the plant may not flower. They should not be exposed to direct sunlight, however, because it can burn the delicate leaves.
Potting and re-potting: Use a soil-based potting mixture and move plants into progressively larger pots as they fill their pots with roots. During the first year, they will probably require re-potting 2 or 3 times, but re-potting is not advisable for Sparmannias in late autumn or winter.
After this, re-potting once a year in the spring should be enough. If left pot-bound, the plant will flower at a younger age. A 10 in (25 cm) pot will accommodate a 6 ft (2 m) specimen.
Propagation: In spring, young stem tip cuttings about 6 in (15 cm) long will root easily either in water or in a moist rooting mixture of equal parts peat and sand.
Use a rooting hormone powder and keep the cutting in a warm place (minimum 61° F (16° C)) where it gets medium light. Move it into a 3 in (7.5 cm) pot of standard potting mixture when it is well-rooted; thereafter treat it as a mature plant. Cuttings rooted in spring will often produce flowers by late winter.
Pruning: Prune after flowering as required to keep the plant under control and in a neat shape.
Temperature: African hemp will stand and benefit from a fairly low temperature in winter, 45° F (7° C) being the minimum. At this temperature, the plant must be left on the dry side, watering about once every 10 days. The maximum summer temperature is about 70° F (21° C), and you should supply some humidity.
Water: Water profusely in the summer, at least every other day. Give only enough water to keep the potting mixture from drying out completely in winter. Once a week should be sufficient at normal room temperature.
Staking is not usually necessary for tall plants, because their stems are rigid enough to support them.
As an Outdoor Plant
Sparmannia africana is not frost-hardy, and in the open garden of a warm temperate climate will grow to 10 ft (3 m) in height. Plant in well-drained, leaf-rich soil.
What Goes Wrong
All leaves drop
Soak plant in bucket of water and never let it dry out
Leaves turn yellow, lanky growth
Move plant to the lightest possible position without direct sunlight
Leaves turn brown in patches and seem scorched
Direct sun on the leaves
Move out of the midday sun
White woolly patches on leaves
Remove them individually with a swab dipped in methylated spirits or spray with a systemic insecticide