Meet Trichocereus
What these ribbed columns are, where they come from, and how they grow.
30-second version first, the whole guide below5 min read
The short version
- You may have walked past one — a tall ribbed blue-green column in someone's front yard, taller than the fence.
- Nearly every one, growers say, is a piece cut from another plant and stood up in soil, and that is the key to how these plants are grown, named and sold.
- In habitat the warm season is the wet one and the cold season is dry.
- A cactus cannot droop the way a thirsty leafy plant does, so, growers say, the ribs do that job instead.
- Real certainty needs flowers or lab work.
Your setup
Pick yours to see what changes in this guide.
Where it grows
In the ground
Nothing in this guide changes in the ground.
In a pot
Dry, they reportedly take nights near 25°F (−4°C); cold and wet together is the danger, so where winters freeze harder growers keep them in pots and bring them under cover.
Where it lives
Outdoors
All-day sun in a high-UV place turns these plants yellow.
Indoors
Nothing in this guide changes indoors.
The season
Winter
In winter they want almost no water.
Not winter
Through a hot summer they reportedly drink far more than a desert cactus does.
Lines are from this guide, or from the cultivar library where one says so. For where they come from, see the end of the guide.
Introduction
You may have walked past one — a tall ribbed blue-green column in someone's front yard, taller than the fence. Almost none of them were grown from seed. Nearly every one, growers say, is a piece cut from another plant and stood up in soil, and that is the key to how these plants are grown, named and sold.
Not a desert cactus
Botanists describe as a group of columnar cacti from the Andes, the high country down the western side of South America. Home there reportedly means real rainfall, heavy dew and cold nights. Nothing like the hot sand people picture.
In habitat the warm season is the wet one and the cold season is dry. So:
- Through a hot summer they reportedly drink far more than a desert cactus does.
- In winter they want almost no water. Dry, they reportedly take nights near 25°F (−4°C); cold and wet together is the danger, so where winters freeze harder growers keep them in pots and bring them under cover.
The parts, and what each one tells you
Five words cover nearly everything on a listing.
- Rib: a vertical ridge running up the column. Ribs work like accordion pleats. Squeezed and sunken means the plant is running low; spread wide and flat means full, growers say.
- — the felted spot the spines grow from. Spines, flowers, fruit and new branches all reportedly start there, nowhere else.
- A notch is the dent on the rib just above each areole. Its seagull shape, wings up, is the usual guide to which end of a is up, growers say, but it varies from plant to plant; marking the top when you make the cut is the sure way.
- , the powdery blue-gray bloom on the .
- Tip: the growing point at the top, where the column gets taller.
The rib trick is the most useful thing here. A cactus cannot droop the way a thirsty leafy plant does, so, growers say, the ribs do that job instead.
Interactive
The parts of a column cactus
Tap or tab through the labeled points. The slider underneath squeezes the ribs from full to thirsty, which is the reading you will use most often.
Part 4 of 9
Rib
The ridge running the length of the column. Ribs work like an accordion. Squeezed together means the plant is thirsty; spread wide and flat means it is full.
Full. The column is holding all the water it can, and the gaps between the ribs are at their widest.
Rib. The ridge running the length of the column. Ribs work like an accordion. Squeezed together means the plant is thirsty; spread wide and flat means it is full. Ribs: Ribs spread wide and flat.
Figure
One areole, close up
This is the one structure the whole plant is built out of, at the magnification a loupe gives you.
- The notch the seagull
- Wings up. On a cutting with nothing else to go on, this is the usual guide to which way up it goes; marking the top when you cut is the sure way.
- The felt pad the areole itself
- A compressed shoot. Every spine, flower and pup this plant makes comes out of one of these.
- Radial spines short, flat, many
- The fan lying close to the skin. Longer in full sun than in shade, on the very same plant.
- The central long, stout, one
- Stands out of the middle, clear of the rest. Counted separately from the radials, and that is how species are told apart.
Farina
the bloom
A waxy powder the plant makes itself, and its own sunscreen. It comes off on a thumb in the shape of the thumb, and it never grows back on that spot.
The growing tip
from above
Areoles laid down on a spiral, crowded and woolly at the center where the spines are still short. The gray woolly spot low on the left may become a flower.
Untouched
bloom intact
One swipe of a thumb
bloom removed
Growth happens in two places
A column gets longer at the tip and branches at the areoles. Mix the two up and you will worry over nothing.
A tip that stops getting longer has terminated. Nothing is wrong, growers say: the tip keeps fattening and the plant branches instead. Cut a healthy column and it reportedly answers with two or three new heads. A cutting makes more plants, not one less.
Speed depends a lot on where you live.
- A grower in San Diego reckons on one to three feet a year.
- In Barcelona, a grower measured 22, 20 and 17 inches on three plants in one season. Moved north, the same collection ran at under half that pace.
- In the wild they reportedly reach about six meters (about 20 feet) before the wind snaps them, and the fallen pieces root where they land.
Arrival day
one head
Twelve months later
one head · one pup · a season of column
The four names you will see
Four species are named most often, and growers tell them apart by rib count, spine length and skin.
- : growers describe six to eight broad rounded ribs, short sparse spines, matte green skin. This is the plant most people mean by San Pedro.
- : growers give six to nine ribs, with longer and stouter spines and often a strong blue bloom.
- : growers say usually four to eight ribs, areoles set well apart, spines long and needle-like.
- : growers note very few ribs, essentially no spines, and a glossy green skin with a melted look.
Figure
The same four, sliced through
Rib count and rib shape are easiest to see from above, so here is each one in cross-section, drawn to the counts and spine habits growers actually go by.
Trichocereus pachanoi
6–8 ribs · broad and rounded · short, sparse spines
Trichocereus peruvianus
6–9 ribs · deeply cut · long stout spines · blue bloom
Trichocereus bridgesii
usually 4–8 ribs · areoles far apart · long needle spines
Trichocereus scopulicola
usually 4–6 low ribs · smooth glossy skin · nearly spineless
Treat that as a rough guide. The species grade into one another in the wild, growers say; they look different young and mature, and sun, water and age move every feature. The naming has been revised more than once and is still argued over. Under recent revisions is the older, senior name, and much of what the trade calls peruvianus would fold into it. Growers still use macrogonus, pachanoi and peruvianus every day.
Why I will not name your plant from a photograph
Rib count, color and spines all move with age, sun and water, on one and the same plant, growers report.
Grown in full sun
short · fat · pale · tight areoles
Grown under shade
tall · slim · dark · areoles apart
One clone, planted in a row, can reportedly show six, seven and eight ribs on identical genetics. That finishes rib count as an ID tool, and color with it. Everything else moves with conditions and age. Real certainty needs flowers or lab work.
So I will not put a name on your plant from a photo. Every name on this site is the label the plant arrived with, and I will tell you what is known about it.
Common mistakes, try it, quick check and sources
Quick check
Question 1: Where does a new branch come from on a cactus like this?
Question 2: The ribs on your plant have squeezed together and look sunken. What is it telling you?
Question 3: A photograph on its own can tell you exactly which clone a plant is.
