Forgive me for not looking it up, but im rather busy at the moment.
Exclude the following species-baldanium, mihanovichii, horstii.

saglionis is afaik the largest growing Gymnocalycium, if cared for properly it is also pretty fast. Mine got sunburnt once too often in its main growth point and it has started showing some weird growth behavior, but it is about a foot plus tall and a foot wide,
multiflorum also gets pretty large and another that is getting pretty large for me, but not quite as fast is G. pflanzii var. marquezii.

I have a G. spegazzinii, that is has gotten very tall, but that certainly is not fast.

The problem is that many of them start offsetting and while the main plant continues growing all the offsetting definitely puts a brake on the speed of growth. If you want one that offsets prolifically look for something called G. anisitsii var. multiprolifera. While none of the individual offsets are huge, the number of offsets has made that plant quite large and it also grows quite quickly. I'd post a picture but for some reason that plant has been really photo shy.

What about bruschii? Seen that one offset a lot in photos.

I had that (well I bought it as G. doppianum, but when it flowered, well it was not doppianum flowers have very different colors), but it did not make it one summer. Happens here. Yes it offsets, but it never was really big for me, not like the three I mentioned in the previous post. So if you are going for big individuals those are definitely winners in terms of size and relative speed. If you want big in terms of offsetting there are definitely different ones to look for.

Offsets or not, clusters can get bigger than an individual plant in some cases....and there are multiple blooming heads. I did say or fastest growing after all... offsets included. Another one that i was eyeing is ragonesei, and ive been told is more durable. However, the specimen i was shown had branches and offsets, https://st.hzcdn.com/simgs/32c... whereas most photos show it solitary.

I think I would put that one under the not very fast growing category offsets or not. Pretty plant though. I like the Gymnocalyciums a lot, have only ever lost a couple of them due to too much neglect, most have been pretty easy plants to grow for me, flower readily and many have great stress colors.

From my perspective, they are not the most prolific offsetters - give or take a few exceptions like for example the G. anisitsii var. multiprolifera I mention above - but as you say when they do offset it increases the areas where flowers appear.

What about saglionis? Isnt that one the biggest? Have any experience with that one?
I think i had one, but that was before learning how to make proper soil, and clean the old one.

see my first response

So your goal is to collect the biggest, baddest of every type of cactus you can get your hands on?

I would think, considering your limitations on space and inability for proper care, you would find species of cactus that would "fit in" to your particular growing conditions.

Have you ever thought of giving up your fascination with South American cactus and concentrate more on North American cactus. There are some stunning cactus that don't mind spending their winter in the cold and dark because, in their home range, they are buried under snow for a good portion of the winter.

Just curious.

I was sort of wondering the same thing, but there's definitely no harm in knowledge used wisely.

G. saglionis is on the large side but not in any extreme way. Here is the one here just about to flower. I put it in my cactus box (see second picture for perspective) which is generous in size, and it has not become a monster. That space is about 2 feet/60cm wide and not quite that deep. It has a SW exposure so lots of late afternoon sun, and has an overhang above it which blocks most of the rain.

DaisyL, i own a a decent ammount of barrels,a few collumnars, and a lot of oppuntias. But so far, only the tiny uninteresting mammilaria prolifera and the" dont live long" thelocactus setispinus have bloomed from them(and the invasive O.humifusa, but thats a different subject). South american blooms on the other hand.....just one word should explain it. BIG. Ive think that flowers from echinopsis and its subgenera, parodia, rebutia, gymnocalyicum, have been far more common and rewarding , than most NA species that im STILL waiting to reach maturity(some will take a really long time.......).
Baja costero, the way im seeing this image, my take is that the astro. ornatum is about 4-6 in your inches wide. That would make the gymno about 7-9 ?What is that plant next to it?
mcvansoest sorry for that.... i was very tired when writing this....

I was actually thinking a little farther north. Here are some first time bloomers in my cactus garden (latitude 39.5N at 5000 ft.). Echinocereus triglochidiatus (2 inch plant with a 2 inch flower) and two Opuntia (blooming on one rooted pad).


And this is how they spend the winter:

Yeah,ive only seen 3 cases of echinocereus being sold here. Its not manufactured(or very rarely) in dutch wholesale, and the ones ive got are quite ugly, and partially pest eaten. Like i said, ive got the hang of the gritty mix quite recently...... And i know they are slow, and never seen one bloom either. Tried germinating from seed, think i succeeded , but that being said, ive got no IDEA what i have .
As for the opuntias, never seen one bloom from wholesale, and in recent years, they havent been sold that often either......and that involves non hardy cultivars. The hardy ones, im trying from seed, but no seedlings so far. . Bear in mind
- i need a phytocertficate and a lot of money just to import common plants
-local plant production is too random and unpredictable, but mostly is just common stuff
- dutch plant imports only have good stuff in them 1/10th of shipments(and there are 5 or 4 yearly).
- seed selection is VERY limited when it comes to opuntias.
Moral of the story? Consider yourself very lucky with specialist nurseries. The nearest one to me is 200km away, in a different country at that.

Baja, not sure how long you have had your saglionis, but for Gymnos those do get really big. They have one at Boyce Thompson Arboretum that is at least 2 feet tall and a good foot wide. It is an old plant, but compared to most other gymnos I have seen it is definitely in a size class of its own.

Skopje, it is unfortunate that it is so hard to get some of the plants you want. I will say though, my mom gets flowers on her Opuntias that she grows inside on a window sill in Haarlem, the Netherlands, and she most definitely is not doing anything special to them in terms of soil and/or watering, just gives them as much light as she can. So it must be a matter of patience and/or not enough neglect ;)

To me Opuntias are the weeds of the desert, just about every pad that I ever put in a pot became a new plant. These days I just throw anything coming off of my established plants straight in the trash (funny story but my city - Mesa, AZ - does not allow you to put any kind of cacti in the green waste...) just to not create another Opuntia that I do not know what to do with. If it would be easier to ship them internationally, I'd love to send some your way.

Like i mentioned, only opuntia i have blooming on a regular basis is a humifusa. But that one grows invasive in some arid areas in this country anyway.

mcvansoest said:Baja, not sure how long you have had your saglionis, but for Gymnos those do get really big.

My plant has been there about 10 years and it was pretty big when it arrived. I don't imagine it will be getting a whole lot wider. It is being fast outpaced by a Parodia and a Ferocactus I put in that cactus box at the same time. For reference I was going by the size described in my cactus book (Anderson) which pegs them at about 12 inches wide and 15 inches tall. Maybe the one at the arboretum is an extra large version?

Baja, maybe we are talking about slightly different things - as a ball shaped cactus comes it is certainly not among the largest that are out there, but as Gymnocalyciums come, saglionis is afaik the largest growing one within the genus.

I have mine in the shade now, because ever since it got the sunburn damage in the growth point it has not been growing that well and starting to look a little misshapen. I hope that the shade will give it some time to recover.

I finally managed to get a picture of my G. anisitsii var. multiprolifera:


And here is my largest G. multiflorum, which is making offsets iso flowers, but other than that it is growing pretty quickly:


And to finish a combo pot with 5 different Gymnocalyciums, the one in the back is another multiflorum (edit: well, I guess I should say it is G. monvillei until I know it is flower color as multiflorum is often considered part of the monvillei group of gymnos that are pretty variable), that is actually G. monvillei that is definitely growing faster than the others though the really spiny one is also not slow:

Those are some really nice looking cacti, Thijs. The first one looks like it is busting out on all sides and will only get more gnarly with age.