San Pedro monstruosus: Trichocereus pachanoi in knobbly form
Trichocereus pachanoi is the columnar cactus known in the Andes as San Pedro. Current taxonomy often files it as Trichocereus macrogonus var. pachanoi, and you will also meet it under the name Echinopsis pachanoi. The species grows wild in Ecuador and Peru at altitudes of roughly two to three thousand metres, and it is now found in Bolivia, Colombia, central Chile, the Canary Islands and mainland Spain as well. In the wild the ordinary form reaches three to six metres, with stems six to fifteen centimetres thick and usually six to eight ribs; the tallest specimen on record passed twelve metres. The whitish areoles sit about two centimetres apart and carry up to seven yellow to brown spines of no more than two centimetres, which on cultivated plants are often shorter still or practically absent. On mature plants, white flowers of nineteen to twenty-four centimetres long and up to twenty centimetres across open at night and carry a strong scent; they last about two days. An oblong dark green fruit of five to six centimetres follows, which bursts open to show white flesh with small seeds. Names used for the species in the Andes include achuma, huachuma, wachuma, aguacolla and giganton.
What sets the monstrose form apart
This plant is the monstruosus form of that species, and it looks nothing like it. The crisp ribs are gone; in their place the cactus builds short, thick segments covered in knobbles that grow above and beside one another. On the product photo you see a light green specimen with two upright arms and hardly any visible spines, rooted in a nursery pot. Monstrose growth takes a different course in every plant, so the specimen you receive will never match the photo: that comes with the form and is not a flaw. Expect a slow grower too, as monstrose cacti rarely shoot upwards.
Care in five points
- Light: as much as you can give it, ideally in front of a south facing window. Too little light turns the growth pale and floppy.
- Soil: a mineral cactus mix with plenty of coarse sand, perlite or pumice, in a pot with drainage holes.
- Water: during the growing season only once the pot is bone dry, roughly every ten to fourteen days.
- Winter: keep it cooler and drier, cutting back to once every three to four weeks or less.
- Repotting: in spring, as soon as the roots fill the pot, then leave it dry for a week.
Root rot is just about the only thing that finishes off a cactus like this, and the cause never varies: watering too often in soil that holds moisture. The knobbly shape makes it easy for water to sit between the segments, so pour along the rim of the pot rather than over the plant.
More cacti at Avalon
Beside this monstruosus, Avalon Magic Plants stocks the ordinary San Pedro, the Peruvian Torch in a small and a large size, the Bolivian Torch, the penis cactus (the monstrose Trichocereus bridgesii) as a cutting and rooted in a pot, the Cuzco, the Macrogonus and seeds of Trichocereus bridgesii. If you would rather start from scratch, there is a complete grow set for cactus seed. All plants ship discreetly packed.
