Pilosocereus pachycladus
| Light | Full sun to very bright light; the bluest colour develops in strong sun |
|---|---|
| Water | Moderate in warm growth; allow to dry between waterings, keep dry in winter |
| Soil | Fast-draining mineral mix (see Soil and potting mix) |
| Temperature | Keep above about 5 °C; USDA zones 9b–11 |
| Propagation | Seed and stem cuttings |
| Toxicity | Non-toxic to cats and dogs |
Pilosocereus pachycladus is a tree-like columnar cactus from eastern Brazil, celebrated as the blue torch cactus for its striking powder-blue stems set off by clusters of golden spines. In good light the waxy bloom on its ribs turns an almost electric silvery-blue, making it one of the most ornamental of all the columnar cacti and a centrepiece plant in collections and warm-climate gardens alike.
Description
Pilosocereus pachycladus is a large, branching cactus that in habitat becomes a small tree several metres tall, forming an upright candelabra of thick stems from a short woody trunk. The individual stems are stout and strongly ribbed, and it is their surface that makes the plant famous: a dense waxy coating gives them a vivid blue to blue-green colour, most intense on plants grown hard in bright light.
The ribs carry closely spaced areoles bearing spreading spines that range from pale to a warm honey-gold, contrasting handsomely against the blue skin. As stems approach flowering size they develop a lateral zone of long woolly hairs — the cephalium-like flowering region typical of the genus — from which the flowers emerge. Blooms are funnel-shaped, greenish-white to pale, and open at night, when they are visited by bats; they are followed by rounded fleshy fruit.
Distribution and habitat
The species is native to eastern Brazil, where it grows in the dry caatinga scrub and on rocky outcrops across several states. It favours hot, seasonally dry sites with sharp drainage, often rooting among rocks in thin gritty soils under strong sun.
Across its range the plant experiences a long warm growing season with summer rains followed by an extended dry period, a rhythm worth remembering when watering plants in cultivation.
Cultivation
Pilosocereus pachycladus is one of the more forgiving columnar cacti, but the intensity of its blue colour depends directly on light — grow it in full sun or the brightest position you can offer, and the waxy bloom will develop to its fullest. In weaker light stems turn greener and grow softer and more elongated.
Use a very free-draining, mostly mineral mix and a pot that drains freely. Water moderately through the warm months once the soil has dried, then reduce sharply and keep the plant dry through winter, especially where it is grown cool. It resents cold, wet conditions above all; protect it from frost and let it stay dry when temperatures drop. Handle the plant with care, as the golden spines are sharp and the waxy bloom can be marked by fingerprints. See Watering and Repotting for general technique.
Propagation
The species is readily raised from seed, which germinates well on a warm, mineral surface kept humid; seedlings are relatively quick for a columnar cactus. Established plants can also be propagated from stem cuttings — a length of stem is severed, allowed to callus for a week or more in a dry, shaded spot, then set on a gritty mix to root. See Propagation — seed and Propagation — cuttings for full walkthroughs.
Common problems
- Rot — the main killer, almost always from overwatering, a slow-draining mix, or cold wet conditions in winter; stems soften and discolour, often from the base.
- Loss of blue colour — too little light greens up the stems and causes weak, etiolated growth that never develops the prized bloom.
- Corky or marked skin — the waxy coating is easily scuffed and fingerprinted, and old growth naturally corks at the base with age.
- Pests — mealybugs (white fluff in the areoles and around the roots) and red spider mites are the usual offenders; see Pests and diseases.
See also
- Pilosocereus — the genus overview
- Soil and potting mix · Watering · Propagation — seed · Propagation — cuttings · Repotting