Pachycereus marginatus
| Light | Full sun to bright light |
|---|---|
| Water | Moderate in warm growth; keep dry and cool in winter |
| Soil | Fast-draining mineral mix (see Soil and potting mix) |
| Temperature | Best above freezing; tolerates brief light frost; USDA zones 9b–11 |
| Propagation | Cuttings (very easy) and seed |
| Toxicity | Non-toxic to cats and dogs |
Pachycereus marginatus is a tidy, ribbed, columnar cactus from central Mexico, best known as the Mexican fence post cactus. Its slender green stems are lined with neat, continuous rows of white-felted areoles running down the rib edges, giving each column a crisply pinstriped look. Because it grows straight, branches sparingly from the base and roots readily from cuttings, it has been planted for generations as a living fence — the origin of its common name.
Description
Pachycereus marginatus forms erect, dark green columns that can reach several metres tall in the ground, usually branching low and staying relatively narrow. Each stem carries five to seven prominent ribs. The most distinctive feature is the areoles: set close together and often merging into an almost continuous white or pale felted line along the crest of every rib, so the whole column appears outlined in fine woolly stripes. Spines are short and modest, more decorative than fierce, and tend to be more conspicuous on young growth.
Mature plants produce small, funnel-shaped flowers along the upper stems in spring, greenish to pink and rather understated compared with the showy blooms of many cacti. These are followed by small, spiny fruits. The plant was long placed in its own genus, Marginatocereus, and has also been treated under Stenocereus, which explains the several names it travels under.
Distribution and habitat
The species is native to central Mexico, where it grows on rocky slopes and in dry scrub. It has been cultivated so widely and for so long — commonly as boundary hedging around fields and homes — that its exact original range is somewhat blurred by centuries of planting. In habitat it enjoys strong sun, sharp drainage and a pronounced dry season.
Cultivation
This is one of the easier and faster columnar cacti to grow, which is a large part of its enduring popularity. Give it a very free-draining, mostly mineral mix and as much sun as you can offer; strong light keeps the columns compact and the rib stripes bright. Water moderately through the warm growing season once the mix has dried, then keep the plant dry and cool over winter to prevent rot and firm up the growth.
It is more cold-tolerant than many desert cacti, shrugging off brief light frost once established, but it is safest kept above freezing in cultivation. In containers it appreciates a heavy pot for stability as it gains height, and occasional repotting into fresh gritty mix. See Watering for general technique.
Propagation
Propagation is refreshingly simple. Stem cuttings root quickly and reliably: sever a length of column, let the cut end callus and dry for a week or more in shade, then set it in barely moist gritty mix until roots form. This ease of rooting is exactly why the species became a traditional living fence, since a row of cut stems pushed into the ground will simply grow. It can also be raised from seed, though cuttings are far quicker and give a fence-worthy plant sooner.
Common problems
- Rot — the usual hazard, brought on by overwatering, a slow-draining mix or cold wet conditions; stems soften and discolour, typically from the base.
- Etiolation — too little light makes new growth pale, thin and weakly ribbed, spoiling the neat striped outline.
- Pests — mealybugs (white fluff tucked into the areoles) and scale are the most common; red spider mites can bronze the skin in hot, dry, still air. See Pests and diseases.
See also
- Pachycereus — the genus overview
- Propagation — cuttings · Soil and potting mix · Watering · Repotting · Pests and diseases