These little cacti are favorites for almost all collectors; I can’t think of any growers I know who don’t have at least one in their collection (or had one at some point, anyway). The lack of spines, the alien-like appearance, and something about how sculptural they appear is deeply attractive to many, many cactus and succulent lovers alike.
There’s also about a million and a half articles about growing them, so I won’t go too much into depth about that. They are relatively easy, and as far as learning to grow species with a distinct cold weather slow down or are less forgiving than, say, an opuntia, these are the training wheels of “fancy” cactus. I’ll run through a quick overview of requirements, explained from the perspective of what I wish I’d known when I got my first few, and then dive into my few cultivars and the growth I’ve seen in my plants over the last 5+ years.
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Natural Habitat
In the wild, you can find these primarily in the center and north of Mexico, as far south as San Luis Potosi and northeast into the Tamaulipas region.
Grows primarily in rocky soils in scrubby plains, often near Agave lecheguilla which acts as a protective cover for young plants. They are fairly abundant and have a wide range, but as with all desirable cactus species, they’re heavily threatened by human development and poaching.
Fortunately, they are extremely easy to grow in cultivation, making collection in the wild unnecessary. You can often find seeds available with locale or collection data, such as those offered from Mesa Garden. These indicate a specific clone or appearance from plants in a specific area, and can help identify plants likely to develop a certain apperance (height, white speckling, pronounced ribs etc).
Basic Cultivation
These are excellent candidates for growers looking to expand their skills beyond the easy to cultivate, fast-growing species such as Opuntia or Echinocereus. Unlike the faster growing species, it’s often hard to tell that an Astrophytum is beginning to fail to thrive until it’s too late.
Soil and Potting
Even large and tall specimens have relatively small root balls, and rarely do these cacti need particularly large pots.
If you’re new to the species, pot them in containers only an inch or two bigger than the largest part of the cactus. By the time it needs to be repotted (roughly every 2 to 3 years), you’ll be able to tell if it’s ready for a new, larger pot or not.
One of my tricostatum clones in a 4″ terra cotta pot, February 2022.
Same plant, November 2022. The following spring I repotted both of my “tripods”.
When it comes to the soil you grow them in, they’re not terribly fussy as long as it drains well. You need to consider your ambient humidity and personal propensity to over water when mixing up your soil.
I’m often an over-waterer, especially early in the growing season, so I trend towards a 75% pumice mix with 25% cactus soil. Lately, I’ve been dropping my pumice to about 50%, and then mixing 25% orchid bark and 25% cactus soil (EB Stone or Miracle grow, as examples).
Many folks use the super-gritty mixes found on Amazon (such as Jack’s Gritty Mix), where they may have little to no organic elements at all. If you’re growing 100% inside and intend to fertilize your plants on a schedule, this may work for you! I find it very difficult to grow these for long on a purely inorganic soil, although it works well if you’re rooting a freshly imported or degrafted cactus. But…in my opinion, it’s just as effective to use pure pumice rather than a fancy rock mix.
If you’re growing outdoors, especially in climates where it’s very hot and you’ve got them sheltered from summer rain – you’ll need some organic material in your soil blend to ensure your cacti can access enough nutrients and moisture during their primary growing season. I fall into this category, and it’s what I’m most familiar with.
You’ll notice that what I don’t say is to pot them directly into a bag mix of cactus & succulent soil. They do need to have a higher inorganic component to their soil mix, and this is a major reason I suggest them as a great candidate for growers looking to expand their skills. For long term growth and best appearance, they need a mix that’s low on the organic material. Too much rich soil can quickly cause rot, or result in a highly stretched, deformed plant that is doomed.
Light
Because these cacti often grow sheltered by agaves or other plants in habitat, they don’t require full desert sun exposure to thrive. They do require extremely bright light to look their best, which can mean different things based on where you’re growing your plants.
In Inland San Diego, where I’m based, these do best in partial shade. I position mine to grow with shade for at least part of the afternoon during summer. Closer to the coast, where folks get more cloud cover and milder temperatures, I know many growers keep them in almost full sun.
If you’re in a more northern climate, you’ll need to learn to adjust your placement based on light exposure. (Again, why this is a great step into more advanced cactus growing!)
Because these are a summer-growing species, those in northern climates have options. You may need to supplement with grow lights for 3 to 6 months out of the year, moving them from indoors to (sheltered) outdoor placements.
An exceptionally well grown, beautiful specimen from the SDCSS summer show & sale in 2023.
The plant pictured above, from the SDCSS show and sale, shows rings of growth pattern that may point to varying levels of light exposure. The areas with intense white stripes are when it was brighter and sunnier. The non-white covered areas are from shady or cloudy periods.
That’s entirely hypothetical, of course – I wasn’t able to talk to the grower, but based on my own plants, it’s my theory. You may be able to mimic a similar pattern, or you may not. You might just accidentally under or over-expose your plant to light, and burn it or cause it to rot out.
Looking greener in October, 2022. I was watering and fertilizing more often that year, and this was in a shadier placement in the greenhouse (may have been under the benches for a few weeks).
Same plant, June 2023. Stripes from the previous year are visible, but in 2023 we had a long, cloudy spring and I watered very little compared to before. You can see it’s closer to the wall of the greenhouse and in brighter light now.
Water and Fertilizer
The stripes lead into the next phase of care: watering and feeding!
If you’re growing your Astrophytum in a highly inorganic mix (such as a gritty mix from Amazon, or nearly pure pumice) then you’ll need to plan for regular feeding. I’ve seen my plants do the best with a half-strength balanced fertilizer with ratios 1:1:1, given as often as every watering during the early part of summer.
My favorite fertilizer, which I buy in bulk at least twice a year, is this classic all-purpose fertilizer (20:20:20 ratio) I’ve linked here. I use it at half strength; you may be able to find it at your local garden shop! All I want is a simple, straightforward water-soluble fertilizer and this has been fantastic at the price.
In spring, I’ll give one or two feedings while the weather warms up and I’m noticing plants are also waking up. Once summer hits and daytime highs for the area (outside of the greenhouse) are routinely in the 80s, that’s when I’ll start feeding about once a week.
As summer reaches the hottest peaks, I scale back my feeding a bit to avoid burning the cacti. While they do thrive with plenty of nutrients and water in excellent growing conditions, they also pause on active new growth or otherwise protect themselves from extreme weather.
A rough schedule of watering and feeding for me, here in San Diego (close to ideal climate for the species):
- January: Keep dry; no water, no fertilizer. Biggest frost risk, must be bone dry.
- February: Continued dry conditions. Some frost risk, keep dry.
- March: Watch the weather. Near the end of the month, might splash the plants.
- April: First “deep” watering whenever the first 3 day stretch in the 70s occurs. Fertilize once if there’s a few days with at least one day above 80.
- May: Water when completely dry. Hot years, this is weekly, fertilizing every other week. Cold/cloudy years means only one watering for the whole month, and no fertilizer.
- June: Water when dry, usually once a week. Feed every week. If it’s a cloudy/cold year, no fertilizer, and water only if bone dry – maybe just once a month.
- July: Water every week, preferably in the evening. If mild (daytime highs below 95), fertilize weekly.
- August: Water every week, preferably in the evening. Feed once, maybe, if there’s no heat wave.
- September: Water every other week if dry/hot. No fertilizer.
- October: Water every other week if daytime highs are still 80+. No fertilizer. Watch for nighttime lows; consistent drops below 50F are the signal for even less water.
- November: Water once, maybe, if nighttime lows are still above 50. No fertilizer.
- December: No water. Frost risk. Splash with water (not a drench, just moisten the soil) if daytime highs reach 80+.
Flowers, Pollination, and Seed Collection
Astrophytum myriostigma will start to bloom in spring, and when they’re happy, they will bloom all summer long and into fall. It’s one of the reasons to fertilize during the time of year when growing conditions are best: they’ll reward you with round after round of flowers, which in turn, will lead to seeds!
Pollination is easy if you’re around to see the flowers open, because they only open up fully when it’s warm and sunny.
Using a small paintbrush, q-tip, or your finger, gently brush around the base of the flower where the powdery stamens are happy to drop pollen on you. Rub the pollen-collecting-recepticle on a flower from a different plant, and then collect pollen from that plant and repeat with the first.
You do need to have two blooms from different cacti fully open at the same time for successful pollination; they are not self fertile.
For the best results, repeat the process about an hour later.
In a greenhouse, you can be very precise, and ensure you’re selecting for certain traits (such as variegation, three or four lobes, etc). If you’re growing your plants outdoors, exposed to the air, it is much more of a crapshoot.
You see, if you have more than one species, these plants are little pollen sluts. They accept pollen like a hipster pizza parlor offering toppings: anything goes, regardless of quality, what you asked for, or if it was even a good idea in the first place.
In particular, Astrophytum asterias, Astrophytum ornatum, and Astrophytum myriostigma swap pollen and cross-breed as enthusiastically as rabbits. If you have your collection outdoors, the only way to be sure you’re not getting cross-pollination is to cover the blooms or know for 100% certainty which blooms were only open for the same species.
Hybrids!
At right are several hybrids from an accidental cross of my A. myriostigma to my A. ornatum, resulting in some very myriostigma-looking seedlings that began getting spines and growing faster than they should have.
A few ways you can spot a possible hybrid is by number of lobes, especially if it’s more than the 5 this species is known for. It’s not impossible for a ‘freak’ to come out in a seed batch with more, but it seems to be far more common for them to have fewer lobes than more.
Seeing spines is also a pretty big sign, although not 100% guaranteed. Very young plants will occasionally produce a couple spines, even in ‘pure’ seed, but they often disappear as the cactus gains some size. By the time a plant is large enough to be potted in a 4″ pot, there should be no spines.
*the fruit does get a spiny-ish covering to protect it when ripe
Producing, and growing, hybrids is not a bad thing in and of itself. The only time it matters is if you’re selling seed (as I do, from time to time) or are trying to produce plants of a specific appearance. If you’re aiming to produce seed (and plants) that are exclusively from cacti grown from locale-specific seed, you’ll care a lot about the accuracy of your pollination program. If you’re trying to select for nudum, tricostatum, or variegata cultivars, being precise in your pollination and seed collection is critical.
All that to say: hybrids are fine, if labeled as such. Be aware that unless you’re pollinating in a closed greenhouse/indoors (where not even bees can get in!), the plants are extremely likely to be pollinated by whatever is blooming at the right stage at the right time.
I purchase, and use, little jewelry bags to cover my flowers and seed pods when I’m trying to be specific about what I’m crossing. Even in my greenhouse, I get bees visiting, and have been surprised at the level of pollination I see in unprotected plants of other species. If I’ve offered Astrophytum seeds or seedlings, I take care to label how they were pollinated and what they were pollinated with.
Admittedly, it’s almost always a crapshoot of same-species concurrent blooms, but if the fruiting plant has a characteristic, that’s what I’ll label. If you see me offer variegated, onzuka, tricostatum etc seeds – that means the seed came from the fruit of a plant with those traits. I’m not a large enough grower to have multiple plants of specific cultivars all blooming at once, so it’s a bit of a lottery as to what you may get (and I price my seeds as such!).
Growing From Seed
When it comes to growing from seed, I detailed the process I follow pretty extensively in my post about Astrophytum asterias.
The most significant difference I have noticed in Astrophytum myriostigma vs. Astrophytum asterias is that they tend to be similarly sensitive at early stages. They need to have high humidity (either from bottom-watering or being covered and still receiving bright light) until they first start to resemble tiny little cacti.
Compared to asterias, I find the myriostigma to be more robust. I’ve been able to start seeds as described, and then move them out to my greenhouse to the floor under the benches within 2 weeks of germinating with decent success.
If you’re more cautious and want to guarantee success, a seed-starting setup similar to what’s needed for successful indoor starting of garden plants is your best bet. I haven’t done this, but several SDCSS club members I know have!
Pests and Treating Them
While not particularly prone to pests, the ones that do get into these cacti are usually sneaky. I find mealy bugs and red spider mites to be the worst, with mealy bugs being my biggest threat. Red spider mites have been a new development, appearing as I started growing in my greenhouse: they are heavily dissuaded by ventilation, and seeing them indicates that the greenhouse hasn’t had enough air movement this winter.
The hardest thing about them is that when you have a plant with lots of white covering it, they can be nearly impossible to spot until the damage is done. Below shows my imported Astrophytum myriostigma cv. onzuka, which came with some signs of mealy damage that became very obvious as the plant grew.
My Astrophytum myriostigma cv onzuka when I first received it as an imported plant, July 2021
In November of 2021 – beginning to see the mealy damage growing out.
Growing out of the damage, May of 2022.
August of 2022, with the new growth looking gorgeous
August 2023 – from the top it looks great. It’s deceptive.
April 2024 – looks like it was grafted, but just outgrowing damage
Treating Mealybugs
The most effective way to treat mealies is to prevent them in the first place: quarantine new plants before adding them to your main collection, and use shade cloth or mesh to enclose your collection if you know they’re a particular risk.
If you, like me, are a regular human being, then you’ll encounter them despite your best efforts.
Seasonally, I perimeter spray the inside of my greenhouse with Talstar (generic version linked here) to create a barrier for ants and other critters coming in. Ants are a big carrier of aphids and mealies, so preventing the ants from getting it is super helpful as a first step. The concentrate can seem expensive, but when you consider the 1 gallon I linked can be converted into 30+ gallons of treatment that’s also useful as a preventative for termites and other household pests…it’s got some expanded uses.
I’ll also use an all-in-one type spray as an immediate treatment for visible mealies, such as the easy to find BioAdvanced 3-in-1. You can try Captain Jack’s, but I haven’t found it to be very effective for mealies in particular. It was particularly nice for my vegetable garden, but for the types of resilient pests that are fond of cacti, it’s not strong enough.
Cultivars
Where do the cultivars for Astrophytum myriostigma come from?
In some cases, you’ll see a particular locale or population number noted on the seeds you buy. Mesa Garden and similar nurseries that specialize in seed will note if a given seed lot is from plants from a given location number.
Varieties, Cultivars, and Locales
Most often, you’ll see seeds offered of a given cultivar or variety.
Mesa Garden seeds, for example, offers varieties (columnar, quadricostatum, nudum, etc) as well as location-specific seed (SB340, SB264).
Location-specific clones can be more desirable, as they’re often harder to come by and be sure of their provenance.
Varieties, or cultivars, are named selections with a specific appearance. Getting seed from a given variety or cultivar doesn’t necessarily mean the plants that grow will be a perfect match!
Astrophytum myriostigma cv. fukuryu is a great example – you’ll readily find various levels of expression for this cultivar, and growing seed from one doesn’t guarantee the seedlings will be the same. They’re more likely to be, yes, but the gene will express differently.
Why get cultivar or variety-specific seed?
If it’s not guaranteed that getting seed from a specific variety or cultivar is going to produce the same look as the parent, why bother?
Because it’s more like stacking the odds in your favor when gambling. It’s not guaranteed to get a fukuryu type variety from any given batch of seeds, but when you’ve crossed at least one cactus showing those traits to another, you’re far, far more likely to see those types of cacti as offspring.
Expanding on the metaphor: it’s a bit like instead of rolling a 6-sided dice and hoping for a 6 every time. Instead, by trying to grow seeds from the particular cultivar or variety you like, you’ve made it so 3 or 4 sides of the dice all say 6. You won’t get a 6 every time, but you’ll get one far more often than a regular dice. That’s why it’s worth getting seed when you know at least one parent plant is the type you want: you’re stacking the odds in your favor.
Astrophytum myriostigma cv. kikko
Astrophytum myriostigma cv. fukuryu
Why do so many cultivars or varieties have Japanese names?
Because the Japanese are unfairly good at this, basically. They’ve been the ones to selectively breed and create many of these cultivars, and as a result, they get to name them.
I will freely admit I don’t know who it is (probably multiple growers) that are responsible for many of the Japanese cultivars that come from that side of the world, but it’s not just Astrophytum myriostigma. There’s definitely a favoring of monstrose appearances, with gnarly, lumpy growth, and then an alternate trend towards thick, fat growth patterns and thick spines (in species that have them).
Contributing factors probably include a climate that’s not well suited to growing these outdoors, so successful Japanese growers likely have their indoor growing setups very well dialed in. Maybe it’s growers based in Thailand or South Korea that are taking advantage of the warm tropical climates to provide longer growing seasons for the cacti – genuinely, I don’t know.
But many of the most desireable and impressive looking cultivars do come from Japan!
I only have a handful, but there’s definitely more out there. Names and their derivatives are related to the number of ribs the plant has (the 5 that are typical, which gets no special name, 4 = quadricostatum, and 3 = tricostatum).
The number of ribs is, as far as I can tell, a roll of the dice. I routinely grow my own seed, of which half my plants are 3 or 4 ribbed plants.
I rarely see more than 1/4 of my seedlings come out with 3 or 4 ribs, which points strongly towards the decreased number of ribs being a happy accident.
This also is a contributing factor to why these oddballs cost more than their 5-ribbed brethren. They’re just plain less common, no matter how much you try.
Variegation seems to follow a similar pattern; despite having multiple variegated specimens, I’ve had even fewer of my seedlings of this species come out as variegated.
To see more varieties, I highly recommend checking out @cactusupdate on Instagram! Alex is lovely, and posts a ton of cool photos and stories.
Interested in some of my seeds and seedlings? Check my shop!
