The unmistakable, beautiful blue myrtle cactus: Myrtillocactus geometrizans!
This species has spawned multiple cultivars, including the ever popular Booby Cactus, and is even commonly used as grafting stock due to how quickly they can grow. They’re striking and distinct, particularly when grown in the light and heat that they so much prefer.
Despite the common name, these aren’t always blue! Compared to a Pilosocereus, they are much more on the green end of the green-blue cactus spectrum.
Species Description and Types
The normal species is a highly branched, columnar cactus that strongly resembles a shrub-like tree when planted in ground and left to its own devices. Flesh is generally a blue-gray, although with plentiful shade, it tends to turn green. They develop a light glaucous coating, particularly if the temperatures and light exposure are ideal. Areoles are spaced decently far apart, about 1 – 1.5″ inches. Typical spines are three to five per areole, but some may have more, up to 9.
Flowers with small, greenish-white flowers that have minimal scent. Starts blooming once it’s about 2 feet tall, but cuttings from more mature specimens will bloom at a shorter height. Produces small, blueberry-like fruits with dark flesh.
Cultivars
Cristatus: There are two types of crested Myrtillocactus that I’ve seen – a smooth, almost spineless form, and a densely spined form that is often labeled as monstrose rather than crested.
“Smooth” form cristata – grown outdoors in full sun, it still develops spines, but they are quite small compared to the normal form.
The more densely crested/monstrose form, with plentiful spines. Compared to the “smooth” form or normal variety, this grows much slower.
M. geometrizans cv. ‘Fukurokuryuzinboku’: a Japanese monstrose cultivar that has a very distinct growth pattern with uniquely shaped ribs.
Care is nearly identical to the normal form, and they eventually do produce arms which can be cut and used for propagation, but as far as I’m aware they do not reproduce true to type through seed.
These are most commonly found in cultivation as fresh imports from Thailand or a similarly warm, semi-tropical climate. They’re freshly rooted, but roots are sterilized and practically dead when shipped – so many novice growers find themselves struggling with these comical plants.
M. geometrizans “dwarf” form – a distinct variety that is smaller in nearly all dimensions except for spines.
The flesh is the same blue-green color, with a slight glaucous coating, but the limb size is significantly smaller, and the plant itself overall reaches a smaller size.
If this looks extremely similar to the Booby form, you’re not the only one to think so – but these do not get the distinct breast-shaped areole growths. These are uncommon, and were originally found in San Luis Potosi, Mexico – although I only have this site to back that up, so don’t quote me.
Care is identical to the nominate form of the species.
Distribution and Habitat
Widespread throughout the central Mexican states, the species itself is quite common throughout Mexico.
Generally grows between 3,000 and 6,000 feet above sea level, in very dry (xerophyllous) scrub land and less often in grassland near the Chihuahuan desert. They’re also readily found in the Mexican tropical deciduous forest, and with the range of moisture they’ll accept in the wild, it’s easy to see why they’re so easy to care for in cultivation.
Care in Cultivation
In warmer climates, you have two choices for growing your Myrtillocactus – in ground, or in a pot. They are extremely fast growing and get quite large when planted in ground, so be wary where you plant them if that’s your plan!
In ground, they thrive with regular water in hot summer months. The hotter it is, the more they like it, and the more water they’ll take. If planting a greenhouse-grown seedling in-ground, be sure to acclimate it to full sun before planting it in its final spot. They should be grown in areas that are quite hot, preferably with summer temperatures in the 90s or higher, and close to full sun.
For in-ground plants, keep dry as nights get colder, and restrict water for the coldest months. If kept dry, they can tolerate night time drops to below freezing (the mid to high 20s), but should not be exposed to a hard frost.
When given regular water in the warm months, and provided with full sun, they grow extremely rapidly both in number of arms as well as arm length.
As an example, the gallery below is my in-ground seedling’s growth this year: February, March, and then November of 2021.
Potted Myrtillocactus care
In pots, these are not nearly as fast growing and can seem almost finicky. They need extremely well draining soil, and to be allowed to dry thoroughly before being watered again. Pots should be on the small side for the root ball; a big issue in rate of growth and appearance of the cactus can often be due to an overly large pot for a smaller seedling. When potting up, aim for no more than an inch of additional space in the pot around the root ball.
Intead of an overly large pot, aim for that well draining soil (up to 50% or so pumice can do wonders!) and fertilize a small amount regularly. Use a low-nitrogen fertilizer, and add it at 1/4 strength each time you water in hot months. During winter, cut back watering significantly, and cut back on fertilizing entirely until days are increasing in length.
Depending on your cultivar of crested Myrtillocactus, it can be close to as fast growing as the normal form, or significantly slower. I’ve found the tightly curling form to be slower than the smooth form, which means the same 6″ azalea pot I’ve had mine in since 2019 will be perfectly fine to repot it in with a soil refresh. The smooth form can form beautiful, scalloped looking curves with enough size, and may benefit from more frequent pot upgrades or soil refreshes.
Protect these from temperatures below 32F, and otherwise, keep these nice and toasty. Apart from growing more slowly in a pot, they thrive with the same high heat and bright sun as the in-ground plants do.
You’ll know you have their care conditions dialed in when the new growth they produce is as thick or thicker than their initial stem, as is the case with my Myrtillocactus geometrizans cv. Fukurokuryuzinboku pictured below.
You may recognize this photo from my post about the Booby cacti around this time last year; this is when I first potted this cactus in the new pot (late November 2021).
I kept this plant in my plastic greenhouse over winter, and then in full sun for spring until my polycarbonate greenhouse was built. The move to the “real” greenhouse had a solid impact; growth was faster, thicker, and the cactus is overall more robust looking. This is from November 2021.
Myrtillocactus geometrizans is an easy to grow species – provided you can give it plentiful light and the warm temperatures it needs to thrive.
They are unlikely to thrive indoors, even as windowsill cacti, due to their need for high temperatures during their growing season. If you air condition your home, it’s probably too cold for these. Additionally, unless you have floor-to-ceiling south facing windows, your house is highly unlikely to have enough light for proper growth.
They can, however, be brought inside by a window for the coldest winter months in northern climates, although I highly recommend a dedicated grow light for your cactus if this is more than 2 months a year. It’s important to remember that these are cacti that thrive in extremely hot, extremely bright climates that are closer to the equator than most of us in North America may appreciate – they’re adapted to days of 10+ hours of light the majority of the year. Your winter home temperatures may not be their preference, but you can help them survive the darker times of year with supplemental lighting. Without it, they will be prone to rot and disease, and are unlikely to thrive long term.
