Care Diary – Gymnocalycium mihanovichii and friends

Written ByJen Greene

Posted: September 22, 2020

Gymnocalycium mihanovichii friedrichii – the Purple Moon Cactus

These are the natural colored cousins to the neon pink, yellow, and orange cacti you see grafted on top of a green parent plant at big box stores. I don’t keep any of those as they lack the chlorophyll to thrive when removed from the graft stock, and I’m not yet skilled enough at grafting to try regrafting the little things.

General Routine and Care

I have a few of these gymnos in my collection now, and have successfully produced plenty of seed all through summer 2020!

I acquired my first little Gymnocalycium mihanovichii in the fall of 2017, and did absolutely no research on care requirements because who even does that?

Naturally my first cactus survived anyway, although compared to my newer plants, it has not grown at nearly the same rate nor did it bloom as prolifically. SO…don’t be me. Let’s learn!


I’ve found these to like it plenty hot; they’re summer growers that thrive with plenty of light, heat, and water during the warm months. Remember that I live in the toasty San Diego region, where it’s relatively dry most of the time, so my watering routine tends to be more intense than if you live somewhere with more humidity.


I keep my purple moons in nearly full sun, making sure that they get direct sunlight nearly all morning and into the early afternoon. I watch the cacti pretty closely; when I first picked up my newest purple moons, they were fairly green, so I slowly introduced them to more and more sunlight over time. By the end of summer, they’d turned their current shade of deep purple to maroon.

This exposure to sun and heat encourages the darker coloration, which in turn tends to encourage greater spine growth as well as explosive flowering.


Like my other cacti and succulents, I try to water these in the evening, especially if it will be hot outside. I keep them with my succulents, as those get more water more often and these Gymnocalyciums tend to be quite thirsty. I think. Honestly, they seem to survive everything just fine. I had a cousin to these planted out front at an angle in dry, clay-like soil with nearly full sun and water every 10 – 14 days at best, and it’s still trucking along. I water my potted succulents and thirsty cacti every 2 – 5 days, by comparison.

Basically, when in doubt, wait longer before you water. They’ll be fine. Especially inside. Indoors, they won’t be as warm or exposed to nearly as much bright light as you think, and will need drastically less water than those kept outdoors in hot, dry conditions.

Soil, Roots, and Pots

I started with Miracle Gro cactus and succulent mix and nothing died, so that’s probably okay for you too if you’re just getting started. It does tend to hold water pretty well, so expect to water less often in the beginning. Before this summer, I’d never fertilized mine, and even this year I used a diluted high potassium fertilizer precisely once and the cacti were absolutely fine.

If you want to get fancy with a soil blend, my preferred soil these days is to find an organic, higher quality blend from a smaller shop and mix that with perlite, pumice, and occasionally orchid bark. The goal in mixing bagged soil blends with these other soil ingredients is to improve drainage. For gymnocalycium, I don’t like a mix that is too heavy with inorganics, as in the wild, these grow in conditions more similar to grasslands than true harsh desert (unlike an ariocarpus or astrophytum). Googling photos of plants in wild conditions tends to bring up plants in hard, clay-looking soil, rather than rocks, often with branches and leaves around them.

Smaller Gymnocalycium mihanovichiis seem to have surprisingly small root systems, at least based on the dozens I’ve packaged and shipped out for sale. My older plants, however, do have decent root systems for their size, so the small roots in the plants I’ve sold are probably related to regular watering routines in nursery conditions. This is an important thing to keep in mind when potted and caring for your cactus!  If you’ve recently picked one up from my Etsy shop or a nursery, chances are, it’s lived a pampered life. Give it some time to adjust to a less frequent watering schedule and new conditions.

I like to pot my plants in terra cotta pots, especially when they have roots that are fine and webby like the ones these guys have. I find terra cotta tends to allow moisture to evaporate relatively quickly and evenly, making sure the cacti don’t have soggy feet for too long.

My Plants Over Time

I’ll post the handful of plants that are in this general complex here. My oldest plants are Gymnocalycium mihanovichii (not a friedrichii, at least not what it was labelled as), a Gymnocalycium rotundulum (which I have since discovered is actually Gymnocalycium damsii var rotundulum?), and two Gymnocalycium mihanovichii var. friedrichii that I picked up this spring.


Gymnocalycium mihanovichii 

I have been so mean to this poor thing. I acquired it as a small cactus in a 2.5″ pot along with the rotundulum, and made the mistake of thinking “I’ll remember what this is” when I lost the tag. I did, but mixed it up with the rotundulum for about a year until I found an older photo.

Here’s  the little guy (and the mixup bud) a few months after I got it: 

gymnocalycium mihanovichii

See? Quite purple. This was in February of 2018, with new growth coming in on top. I had this on our back retaining wall, where it would experience light frosts and full sun all winter.

To help emphasize why I confused this with my damsii so consistently for about a year straight, I present the next two photos. The plant below is the same one – the gymnocalycium mihanovichii.

 gymno mihanovichii

This is the gymnocalycium damsii.

gymnocalycium damsii

I tell them apart in photos now through the shape of the spines – my mihanovichii has them pointing almost straight out, while the damsii has them laying flatter, very similar to a gymnocalycium denudatum.

My mihanovichii got hit hard with rust in the winter of 2018 – 2019, and scarred up significantly. Looking below, it’ll look just like the plant has orange dust on it, which is exactly what rust looks like. In winter, the cactus turned this color, and has retained it since. The rust eventually healed, but healed as very noticeable scarring, which you’ll see in later photos. Thanks to the rust, I’ll always be able to tell them apart now!

The photo below is from January/February of 2019.

gymnocalycium mihanovichii with rust

The cure for this, by the way, is simply drying the plant out. The end. Don’t let it sit all soggy. I’m lucky it didn’t rot out!

Here it is about a month later, still rusty:

gymnocalycium with rust

Here’s the scarring in July of 2019, so after it had had a chance to heal and grow a bit. It was still not super stoked about life.

gymnocalycium recovered rust

If you look closely, you’ll see the beginnings of a little flower bud on top! It was still growing, and as you can see, it’s still that bright pink color, rather than the maroon it was when I first got it. By this time, I’d repotted it, and added a layer of pumice on top for dressing.

At this point, the loving abuse begins. Plenty of bright sun, lots of heat, and being kept dry and protected if there’s rain.


Out of focus slightly but you can see some of the growth recovery by January of 2020, where I was much more on guard against rust. If you look closely, though, you’ll see that on the right hand side, some rust is still managing to appear. The challenge with morning dew is that is keeps plants too damp when they don’t like that much moisture! If you’re in a more humid climate, definitely be aware of this risk.

gymnocalycium jan

Here’s the plant in June, after a rather excited month of blooming (during which I brilliantly took no photos?).

I repotted it sometime between June and July, and refreshed the top dressing. At this point, with fresh soil and fresh pumice on top, it was quite happy and began to really grow out the scars.

gymnocalycium top view

And here is my scarred little friend in September 2020, still blooming!

gymnocalycium micho

You can see that the scars are a few spine-rows down, now, and are less prominent than they were before. They’ll never really go away, just grow out to be further down on the plant, so this is unlikely to ever be a pristine specimen.

Gymnocalycium damsii var. rotundulum

I acquired this little guy in the winter of 2017, same time (I think) I picked up my first mihanovichii. I have not been the kindest to this cactus, but it’s been fine anyway. I even have a couple of pups that I’m establishing, so if all goes well, I’ll have seeds or young cacti to offer in my shop sometime soon! 

Ah, pre-COVID days, when you could go to a cactus club and pick up plants in person. 

gymnocalycium damsii

Note the color – it’s primarily green, with a couple small babies on the sides, and deep maroon color blushing in on the spike sides. I thought it’d get a darker purple with time. You saw the photos above when I had it confused with my mihanovichii! 

gymnocalycium mihanovichii

By February of 2019, it had turned this super bright pink color. It also was not at all affected by rust, like the mihanovichii, just stopped growing. 

gymnocalycium damsii

Interestingly, when the weather started to warm up, the coloration became less intense. The photo above is from May of 2019. The weather was warming, although the plant hadn’t quite fully woken up, yo ucan see some green at the top where new growth was coming out. 

gymnocalycium damsii

Later, in October of 2019, you see it had grown (including the pup on the side), but it was…not plump like the photos you may find when googling online. This was about the time when I made the decision to put it in the ground over winter, which surprisingly did not kill it! A later blog post will show what it looks like now, as I pulled it back out of the ground this fall and repotted it again. 

Gymnocalycium mihanovichii var. friedrichii 

So, some tea. 

When googling around about this plant for this blog post, it turns out that this…isn’t really a thing? If you check out my favorite species repository, llifle, it’ll tell you that this is an invalid name that refers to the pink flowered form of Gymnocalycium stenopleurum. It’s sometimes designated as a full species, Gymnocalycium friedrichii, and sometimes it’s just Gymnocalycium mihanovichii, and apparently G. stenopleurum is quite distinct from mihanovichii but the friedrichii is a blend of the two? 

I don’t know. Scientific names aren’t my thing. 

Either way, I have three of these! Two acquired in early summer this year, and another this fall. 

Here are my two from this summer – as you can see, flower color is…questionable. The one on the left I daresay has white flowers, which may be a specific locale? The pale pink flowers of the one on the right are more common and typical of the species. The photo below is from the first week of June, 2020. 

gymnocalycium friedrichii

This is the pink blooming friedrichii about a month later, although it looks pretty darn close to the same as it did in June. It just kept throwing flowers! 

The white blooming plant in mid July 2020. This one was my primary producer of seeds, with the vast majority of seeds germinating. It’s still blooming now several weeks later! 

Thank you for reading! 

And thank you for scrolling through all of my photos! I hope it was interesting and helpful for you. 

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