Ariocarpus retusus
Where are Ariocarpus from?
These fascinating cacti are all from Mexico, with a small overlap up into Texas. They’re highly adapted to periods of drought, using their thick, tuberous roots to hold extra moisture to tide them over until the next rainstorm.
They thrive in rocky soils, often growing on slopes or hills, very similar to how Lithops and mesembs are often found. Most species grow very close to the ground compared to how they are found in cultivation, and may be nearly impossible to see in habitat until they bloom.
Cultivation
Depending on your favorite plant blog, you may hear that these are challenging, finicky plants to grow that take ages and can sometims die for no reason. That…can be true. They’re slow to grow. They will absolutely rot in winter if they’re watered when it’s cold. For a novice grower, it’s easy to go to extremes: I’ve talked to people who under-watered their plants to the point of dessication, and the other way around. Some folks have read the Wikipedia article calling these “succulent, subtropical plants” and took that to mean they need way more water than they do.
If you have the right conditions, or can make them artificially, they’re not particularly challenging to grow, just slow. I’ll detail how I care for mine, and hopefully help you care for these yourself!
Ariocarpus retusus ssp. confusus
Soil for Growing Ariocarpus
Being highly adapted for dry, poor soil, they (as with nearly all cacti) need a very well draining minx. Compared to your typical mammillaria or gymnocalycium, however, they need it even better draining, and even more lacking in organic matter. Using a cactus and succulent mix right out of the bag, without amending it at all, is a pretty good way to rot your cactus. It’s hard to get a mix right out of the bag that’ll stay loose, aerated, and drain rapidly enough to work well.
For my Ariocarpus, I use a mix that’s essentially identical to my mesemb mix. Roughly 50% pumice, 25% orchid bark, and 25% cactus soil.
Pumice is inorganic rock, basically, that is highly porous and (relatively) lightweight. The porous and irregular nature of the rock makes it ideal for keeping a well-draining soil that also allows for airflow around the roots.
As I’ve mentioned before, I include orchid bark in my mix to hold on to moisture a little longer than pure pumice because I keep my plants in my greenhouse where it gets very, very hot. I find even my most arid and drought adapted species do better with the orchid bark in their soil to help give them an extra sip of water through the hottest days.
Lastly, a good cactus and succulent soil is key. I try to steer clear of the miracle grow mixes, as they tend to be higher in organic material than I prefer, and go for a locally made organic blend if I can.
I’ve been asked before about using Bonsai Jack’s mix, and to be up front: I’ve never used it, personally. Looking at the bags and mix, though, I’d classify the “gritty mix” as an amendment – replace the pumice and bark I’m suggesting here with that gritty mix, but still use a more organic soil to add to it. In a pinch, I’ve simply used houseplant soil in a smaller quantity and added a little more orchid bark, and called that good. In my opinion, you do need some small particle organic matter for the roots to have something to “eat” and grow with.
How often should you repot an Ariocarpus?
These are cacti that do well in the same pot year after year after year.
You shouldn’t need to repot your Ariocarpus more often than once every two or three years – usually longer, especially for younger plants, and doubly so if you added the 25% organic matter to the soil I suggested.
You can tell it’s time to repot your Ariocarpus when the pot is bulging at the sides from the tap root, the soil appears compacted, or you’re seeing other issues that require a new pot (you over-potted originally, there’s a pest infestation, etc). Otherwise… leave them alone and let them get big and old in their pots!
Ariocarpus retusus
This doesn’t mean you need to completely avoid repotting them if you would like to change their soil, put them in a nicer pot, or otherwise adjust them. My oldest / largest Ariocarpus retusus, pictured above, was repotted several times before I got it situated in its current show pot and it’s none the worse for wear.
Several of my seedlings and younger plants have also had similar treatment, and while they probably would have been better if left undisturbed – also not that big a deal. Once I figured out the soil mix I liked best, updating all my arios to the same soil just made sense.
My only caveat: don’t repot your Ariocarpus in winter. Wait until late spring or summer. They should be awake, growing, and able to easily bounce back. If I can, I’ll even avoid disturbing these plants in fall (September/October), preferring to give them more time to set up to rest for winter and the long dry period.
Ariocarpus kotschoubeyanus
6 years old (purchased as 2 y/o seedling, 2020)
Watering your Ariocarpus
Even as someone growing my Ariocarpus in a greenhouse in San Diego, I still have to routinely remind myself: I don’t need to water them nearly as much as I think I do.
Much like my mesembs, these are cyclical growers that have distinct growing seasons, and thrive when you respect them. This is particularly the case when you are growing them with access to the outdoors and the natural temperature extremes. Again, like mesembs, these do really well for the average US grower when they are exposed to high summer temperatures and low (but not freezing) winter temperatures.
Ariocarpus fissuratus in bloom
I’ll lead with describing how I water my Ariocarpus, but I’ll emphasize: mine are all in my San Diego greenhouse, reaching daytime highs of 125F regularly in summer, and getting to 32F at night in winter.
I generally follow nighttime temperatures as my cue for when to start or stop watering for a season, and then high temperatures for frequency during grow seasons.
In spring, I wait until nights are pretty regularly at or above 50F before I water them for the first time of the year.
I’ll water once or twice a month while daytime highs are rarely above 80F, and if there’s likelihood of nights dropping back below 50F again. Usually, this means first water is in March or April, and it’s very light until the end of June.
As summer temperatures start to climb, I start keeping a closer eye on the high temps and how the cacti are looking. If they’re nice and plump, I’ll give them a longer period of time before I water again.
With my greenhouse, through June and July, the temperature becomes extremely dependent on how cloudy it is. In 2023, we had a long, gloomy spring, and my greenhouse daytime highs rarely went above 9oF from March through even early July. As a result, I only watered my cacti once or twice a month for that time.
In 2022, though, it was sunny and the greenhouse got hot quickly! In response, I was watering almost every week starting as early as late April. 100F in the greenhouse was an excellent opportunity to “spoil” my cacti and give them a boost before the heat waves that were sure to come later in the year.
Very old and well grown Ariocarpus kotschoubeyanus at an SDCSS show
As the peak summer temperatures hit, you have a choice: water your cacti more often to keep them plump and growing fast, or grow them harder and more naturally.
I always have a hard time resisting the urge to water, but in part, it’s because I know as summer really stretches on – I just won’t want to be up in the greenhouse! It gets so hot all the time, it’s a genuine chore to water in there in August, even at 8 am.
So…my typical yearly schedule with these is to keep up on watering as often as every week in early summer, and I’ll embrace the slump in late summer and let it stress the plants then. That means July is a transition month: sometimes I water every week (if it’s hot), sometimes it’s only every 2 or 3 weeks (if it’s cooler).
August and September are the hottest months for us, and for my seedlings I’ll water even more often, every two or three days. I watch my cacti closely for shriveling or wrinkling, but some stress from underwatering leads to better growth!
If you’re growing indoors under more static temperatures with no real extreme highs or lows, expect to water much less often than I’m describing. Without high temperatures to encourage growth and rapid moisture evaporation, once a month may be more than enough!
Light and Sun Exposure for Ariocarpus
While evolved to thrive in extremely bright conditions, some consideration needs to be given for your specific placement and conditions. Wild plants grow under some shade or shelter, retreat into rock crevices, or get covered by dust, dirt, or debris due to how low they grow to the ground. There’s usually some sort of shade provided for the most intense sunlight in summer, though not always.
An Ariocarpus hintonii at the cactus club show, showing how being kept in one spot and not rotated leads to a natural sun-dial like growth habit as the cactus leaves follow the sun.
Knowing that they aren’t necessarily fully exposed in nature should help you determine where to place your Ariocarpus. Indoor growing means additional supplemental lighting; while these aren’t always exposed to intense, blasting sun, your indoor conditions can’t compare to outdoor sunlight. You can use a light meter to try and measure your light brightness, and compare it to outdoors (even on a cloudy day), and that’ll help you better understand how bright you’ll need to make your lights.
I’ve grown my A. retusas under full sun, and they bronzed considerably. I also sunburnt the bejeezus out of my first seedlings of other species, which is part of why I recommend against full sun for your own Ariocarpus if you’re a beginner. Start with partial shade, outdoors, and monitor your cactus to see how they do.
All of my Ariocarpus are now in my greenhouse, with 40% shade cloth to protect them from direct overhead sunlight. They get more sun exposure in morning and late afternoon, which is enough to keep them growing compactly but isn’t intense enough for them to darken much in color.
An Ariocarpus cauliflower that won first place at the SDCSS show & sale last summer
These slow growing cacti do take longer to demonstrate signs of stretching and low light, and may be harder to identify. Rather than simply stretching, these are more likely to rot or turn to mush if kept with inadequate light (part of why they’re described as harder to grow).
When keeping outdoors in shade, if you can, opt for shade from trees or plants rather than the shade of a building. Dappled shade from plant life is more diffuse, and still allows for more sunlight in a way that’s closer to their natural growing conditions (so you’ll keep that compact growth they’re known for). The more shade your cacti get, the less water they will need, and the slower they will grow. This isn’t necessarily bad, but it should be part of your considerations in caring for your plants.
Fertilizing Your Ariocarpus
If growing your Ariocarpus in a highly inorganic mix as I describe, you’ll need to give your plant some additional food to keep them growing happily in the summer months.
As I recommend for most of my cacti and mesembs, I use a dilute 1:1:1 fertilizer. In spring, I’ll feed once after the first watering of the year, then again a month or two later. When summer is in full swing and it’s over 100F during the day, I use fertilizer nearly every watering (if I remember). I’ll taper off in fall, and stop feeding entirely sometime in September, although I keep watering if it’s hot out.
Osmocote is a slow release fertilizer that is tiny little plastic-looking balls, and can be mixed into your soil at half strength recommended on the bottle when you first pot your Ariocarpus…but it’s not my favorite. If I know I’ll be particularly lazy or traveling and unable to fertilize on schedule, I’ll sprinkle it on top of my pots to tide them over.
You don’t have to fertilize your cacti, but as I do keep mine in a pretty inorganic mix, I find they grow faster and look better with regular feeding than without. After a year or two in the same pot, most nutrients are going to be fully absorbed, so the cacti will need something to “eat” besides water to fuel their growth.
Ariocarpus “maruibo” at the SDCSS show & sale
If you want to encourage your Ariocarpus to bloom and produce seed pods, fertilizing on a regular schedule during the growing season is a good way to do that. You’ll notice in the photos of the show plants and on my own plants that there are little tags on flowers or seed pods – these are to track the various crosses made for producing seed.
Flowering and Seeds
They’re relatively easy to pollinate, using a paintbrush, q-tip, or even tweezers to grab some of the stamens to dust over the pistils. Then…you wait.
When ready, the fruits will be visible and slightly deflated, as seen in the Ariocarpus “maruibo” pictured above. It feels like it takes forever for them to ripen – I haven’t kept close track of pollination to fruit readiness, but it’s taken at least a month or two (I think longer?) for my plants to spit out some ripe fruit.
Harvest the seeds by slicing open the fruit, and scraping them out. I like to scrape onto a paper towel to let them dry and then store them, as the seeds are large enough to easily handle with blunt tweezers. I’ve seen other growers rinse them in a seive with a coffee filter to prevent them from falling through, which helps get all the fruit bits off to prevent rot or mold from growing. For seeds I’m going to sow and grow myself at home, I’ve been fine without doing this, but to sell them it would be a good idea to rinse off what you can.
And that sums it up!
Water them less than you think.
Keep them somewhere bright, but not necessarily in direct sunlight (your mileage may vary).
Let them get hot hot hot in summer, and keep them dry if it’s cold in winter.
And have patience. They take years to grow!
Last, but not least, these are also unfortunately subject to poaching. I talk about this in much more detail when I discussed “hard grown” plants earlier this year.
