Trichodiadema bulbosum
| Light | Full sun to bright light; the more light, the more compact the growth and the better the flowering |
|---|---|
| Water | Moderately in active growth; let the soil dry out between waterings and keep much drier during the plant's rest |
| Soil | Gritty, fast-draining mineral mix (see Soil and potting mix) |
| Temperature | Tolerates light frost (to roughly −4 °C) once established, but protect from hard, prolonged frost; roughly USDA zones 9b–11 |
| Propagation | Seed, or stem cuttings |
| Toxicity | Not known to be toxic to cats or dogs |
Trichodiadema bulbosum is a small, shrubby succulent from South Africa, a member of the ice-plant family Aizoaceae and one of the so-called "mesembs". It is prized by collectors for its swollen, tuberous root system, which growers lift above the soil to create a gnarled, woody base — earning it a reputation as a succulent bonsai subject and the affectionate name African bonsai. Its small green leaves are each tipped with a neat tuft of bristles (the diadem that gives the genus its name), and in season it is crowned with bright magenta, daisy-like flowers.
Description
Trichodiadema bulbosum is a low, spreading, much-branched shrublet, usually only a hand-span tall, with slender woody stems that carry pairs of small, club-shaped succulent leaves. Each leaf ends in a crown of short, soft white bristles — the feature that distinguishes Trichodiadema from other superficially similar mesembs and lends the plants a slightly hairy, crystalline look up close.
The plant's most celebrated feature lies below ground: a thickened, tuberous rootstock that swells with age into a gnarled, barky caudex. Left buried it is invisible, but growers commonly raise it above the surface over successive repottings so that the exposed roots become the main ornamental feature, much like the trunk of a bonsai tree.
The flowers are typical of the family — many narrow petals radiating from a central boss of stamens, opening in bright sunshine and closing again toward evening. They are a vivid magenta to purple-pink, usually with a paler centre, and are borne over a long season from spring into autumn.
Distribution and habitat
The species is native to the Western and Eastern Cape provinces of South Africa (in the region around Port Elizabeth), where it grows in dry, open scrub and rocky ground. Like many mesembs it is adapted to a harsh, arid climate: the succulent leaves and the water-storing tuber allow it to ride out long dry spells, drawing on stored reserves until the rains return.
Cultivation
Trichodiadema bulbosum is an easy and forgiving succulent, which is part of its appeal as a beginner-friendly bonsai subject. Grow it in a very free-draining, mostly mineral mix and give it as much light as you can — full sun keeps the stems short and the flowering generous, while too little light makes the plant sprawl and etiolate.
Water moderately while the plant is in active growth, always letting the mix dry out before watering again, and reduce watering sharply during its rest period; the tuber is prone to rot if kept wet and cold. It tolerates light frost once established, but protect it from hard frost. See Watering for general technique.
To develop the plant as a caudex bonsai, repot every year or two and lift the tuberous roots a little higher each time, gradually exposing more of the woody base. The exposed tissue firms up and barks over with time. Light pruning of the top growth encourages a denser, more twiggy crown to balance the raised roots.
Propagation
The species grows readily from seed sown on a warm, gritty surface and kept lightly moist, in the manner usual for mesembs — see Propagation — seed. It also strikes easily from stem cuttings; allow the cut end to callus for a week or two before setting it into a gritty, sandy mix.
Common problems
- Rot — overwatering, or a mix that holds water, will rot the tuber and lower stems, especially in cool weather; err on the side of dryness.
- Etiolation — in too little light the stems stretch, flowering falls off, and the compact habit is lost.
- Pests — mealybugs (white fluff in the leaf axils and among the roots) and the occasional spider mite are the usual offenders; see Pests and diseases.
See also
- Trichodiadema — the genus overview
- Soil and potting mix · Watering · Repotting · Propagation — seed · Propagation — cuttings