Pilosocereus azureus
| Light | Full sun to bright light; the blue bloom develops best in strong sun |
|---|---|
| Water | Moderate in the growing season, letting the mix dry between waterings; keep dry and cool in winter |
| Soil | Fast-draining mineral mix (see Soil and potting mix) |
| Temperature | Keep above freezing; USDA zones 9b–11 |
| Propagation | Seed; stem cuttings |
| Toxicity | Non-toxic to cats and dogs |
Pilosocereus azureus is a tall, brilliantly blue columnar cactus from eastern Brazil, widely grown and traded for the powdery, almost electric blue-green skin of its young stems. The name is one of the most familiar in the hobby, but botanists now generally treat these plants as part of the variable species Pilosocereus pachycladus (as P. pachycladus subsp. pachycladus), with "azureus" persisting as a horticultural and trade name rather than a distinct species. It is often sold under names such as blue torch cactus and blue columnar cactus.
Description
Plants form slender to stout blue columns that branch with age and, in time, can grow into small tree-like specimens several metres tall. The most striking feature is the colour: new growth is coated in a fine waxy bloom that gives it a vivid silvery-blue to turquoise cast, gradually greening and greying as the stem matures. The ribs are well defined and carry evenly spaced areoles bearing golden to amber spines that age to grey.
As the plant approaches flowering size it develops a cephalium-like zone of dense wool and bristles along the upper stem — a hallmark of the genus Pilosocereus, whose name refers to this hairy flowering region. Flowers are nocturnal, funnel-shaped and pale, opening at night and typically pollinated by bats and moths in habitat, and are followed by rounded fleshy fruit.
Distribution and habitat
The blue columnar cacti gathered under this name are native to eastern Brazil, where Pilosocereus pachycladus ranges widely through the dry caatinga scrub and rocky outcrops of the interior. Plants grow in hot, bright, seasonally dry conditions, often rooted in thin soils over rock, and are well adapted to long dry spells broken by warm-season rain.
Cultivation
This is a fast, rewarding and forgiving column for a hot, sunny spot. Grow it in a very free-draining, mostly mineral mix and give it as much light as you can — strong sun brings out the deepest blue bloom, while too little light produces greener, weaker growth. Water moderately through the warm months, letting the mix dry between waterings, then keep the plant dry and cool over winter to prevent rot and cold damage.
Because it is frost-tender, growers in cooler climates keep it in a container to move under cover before the first frost. Handle young stems carefully, as the waxy blue coating rubs off easily and leaves permanent marks where touched. See Watering and Repotting for general technique.
Propagation
Both seed and cuttings work well. Seed germinates readily on a warm, moist mineral surface; see Propagation — seed. Cuttings are the quickest way to a large plant — take a section of stem, let the cut end callus for a week or two in a dry, shaded spot, then pot it into a gritty mix and water sparingly until roots form. See Propagation — cuttings. This species is also a popular, vigorous rootstock for grafting slower or more delicate cacti.
Cultivars
As a horticultural staple, blue Pilosocereus are selected mostly for the intensity and evenness of their blue bloom, and crested (cristate) and monstrose forms occasionally appear and are prized by collectors. Named clonal cultivars are far less established here than in a genus like Astrophytum, and much of what is sold simply travels under the "azureus" trade name.
Common problems
- Rot — the usual cause of loss, almost always from overwatering, a slow-draining mix, or cold-and-wet winter conditions; the stem softens and discolours, often from the base.
- Cold damage — even a light frost scars or kills the tender blue growth; protect from freezing temperatures.
- Scarred bloom — the waxy blue coating is delicate and permanently marks where rubbed or handled, so it is cosmetic rather than harmful.
- Pests — mealybugs (white fluff in the areoles and around the roots) and scale are the most common; see Pests and diseases.
See also
- Pilosocereus — the genus overview
- Grafting · Soil and potting mix · Watering · Propagation — cuttings · Propagation — seed