Myrtillocactus geometrizans
| Light | Full sun to bright light; tolerates some shade |
|---|---|
| Water | Moderate in growth; allow to dry between waterings; keep dry and cool in winter |
| Soil | Fast-draining mineral mix (see Soil and potting mix) |
| Temperature | Best above freezing; brief light frost tolerated on established plants; USDA zones 9b–11 |
| Propagation | Cuttings (very easy), seed |
| Toxicity | Not known to be toxic; fruit edible |
Myrtillocactus geometrizans is a fast-growing, powder-blue columnar cactus from central and northern Mexico, prized both as an ornamental candelabra plant and as one of the most popular grafting stocks in the hobby. Its branching, tree-like habit and chalky blue-green stems have earned it the common names blue candle cactus and, for its edible berries, garambullo. It is the best known member of the genus Myrtillocactus.
Description
Myrtillocactus geometrizans grows into a shrubby, candelabra-shaped plant that branches freely from a short trunk and can reach several metres tall over time, though it stays far smaller in a pot for many years. The stems are a distinctive glaucous blue-green — a waxy bloom over the skin gives them their powdery, almost frosted look — and are usually divided into five or six broad, well-defined ribs, a geometry that gives the species its name.
The areoles are widely spaced and carry short, dark spines: typically a few small radials and a single stubby central that is often nearly black. Small, creamy to greenish-white flowers appear along the ribs in clusters, several to an areole, followed by small round berries. These fruits, the garambullo, are dark purple, sweet and edible, and are gathered and sold in parts of Mexico.
Distribution and habitat
The species is native to a wide swathe of central and northern Mexico, where it grows on hillsides, in thornscrub and in dry open woodland. It is a plant of hot, seasonally dry country, rooting in rocky or gritty soils and often forming a conspicuous part of the landscape. Its broad natural range and vigorous growth make it common both in the wild and in cultivation.
Cultivation
Myrtillocactus geometrizans is one of the easier columnar cacti to grow and is forgiving by cactus standards. Give it a fast-draining, mostly mineral mix, a generous pot to support its quick growth, and as much light as you can — full sun brings out the best blue colour, while too little light produces pale, drawn stems. Water moderately through the warm growing season once the soil has dried, then keep the plant dry and cool over winter to prevent rot.
The waxy blue bloom on the stems is easily rubbed off by handling and does not regrow on that patch of skin, so move plants by the pot rather than the body. Established plants tolerate a little light frost, but young or potted specimens are safest kept above freezing. See Watering and Repotting for general technique.
Propagation
Propagation is very easy. Cuttings root readily: sever a branch, let the cut end callus for several days to a couple of weeks in a dry, shaded spot, then set it in a dry mineral mix and water sparingly until roots form. Seed also germinates well on a warm, humid surface. See Propagation — cuttings and Propagation — seed for full walkthroughs.
Because it is so vigorous and undemanding, M. geometrizans is widely used as a rootstock. Slow or delicate plants — and many crested or variegated novelties — are commonly grafted onto it to speed their growth.
Cultivars
Several forms are grown for their unusual shapes. The best known is the "Fukurokuryuzinboku" or "Boobie cactus", a lumpy, largely ribless monstrose form whose knobbed stems are popular as an oddity. Crested (fasciated) and variegated forms also occur and are usually maintained by grafting or cuttings rather than seed, since they do not come true.
Common problems
- Rot — from overwatering or a slow-draining mix, especially in cool weather; stems soften and discolour from the base.
- Etiolation — too little light makes new growth pale, thin and stretched, losing the strong blue colour and ribbing.
- Marked bloom — the waxy blue coating is permanently rubbed away wherever the stem is handled, leaving darker green patches; harmless but cosmetic.
- Pests — mealybugs (white fluff in the areoles) and red spider mites (fine webbing, bronzed skin) are the usual culprits; see Pests and diseases.
See also
- Myrtillocactus — the genus overview
- Grafting · Soil and potting mix · Watering · Propagation — cuttings · Propagation — seed