Which are the most slow-growing cactus seedlings?

[Armen Tsirunyan]

So, after sowing cactus seeds for three consecutive years with success, I am planning to delve into the project of growing some of the more challenging species that grow extremely slowly this fall. As of now, my list is comprised of the following:

Strombocactus disciformis
Aztekiums hintonii and ritterii
Blossfeldia liliputana
Geohintonia mexicana

What other species can you suggest that are notorious for slow-growing seedlings?

[mdpillet]

Rimacactus laui is supposedly very hard to grow from seed.

[Armen Tsirunyan]

Rimacactus laui is supposedly very hard to grow from seed.

Good to know, thank you. Although I am looking more for "slow" rather than "hard" per se. I mean, I am in no way going to attempt any pediocacti or such

[greenknight]

Turbinicarpus are a little bit slow - not as slow as the ones you list, though. I don't think anything else is as slow as Blossfeldia.

[Hanazono]

I think each person has different opinion but:

Both of Aztekium hintonii and Geohintonia mexicana glow slowly but they are manageable.
Seedlings of all others are too small and too slow to grow and I could not manage them.

[greenknight]

The only one of the four you list that I've tried is Strombocactus disciformis, and my first attempt failed. My second batch did better, they're 10 months old and the largest is maybe 4mm in diameter (they're still sealed in a baggie, so that's a rough estimate).

[Armen Tsirunyan]

The only one of the four you list that I've tried is Strombocactus disciformis, and my first attempt failed. My second batch did better

So, what did you do differently the second time? Any tips? How many seeds did you sow? How many seedlings did you end up with?

[Armen Tsirunyan]

I think each person has different opinion but:

Both of Aztekium hintonii and Geohintonia mexicana glow slowly but they are manageable.
Seedlings of all others are too small and too slow to grow and I could not manage them.

Thank you, Hanazono. Can you remember, what germination percentage, roughly, have you experienced with A.hintonii and G.mexicana?

[Hanazono]

I bought seeds of these 2 species 2 times and sowed.
The germination rates of these species were around 50% on both times.

The germination rate of cactus seeds is affected by the freshness of the seeds and sowing environment.
Since I bought seed, I did not know the actual quality of the seeds.
You may get a better germination rate.

[greenknight]

As for my Strombo adventures, I don't know how many seeds I planted the first time (in 2014). The seed is like dust, not practical to try and count it. It was seed from Aiko, and he sent a generous amount - they came up thick, I couldn't count them either. Since they would spend a long time closed in the baggie, I thought it would be a good idea to start with a very wet medium, so I wouldn't have to open it to add water. This was a big mistake, they simply failed to grow beyond the early seedling stage. The ones that lasted the longest were on top of chunks of pumice where it was not so wet, but they eventually succumbed, too. As it happened, none of my cactus seedlings survived that year - after I took them out of their baggies, a colony of tiny moisture ants decided to move their nest into them overnight. Not a speck of anything green was left.

The next year, I stuck to easier species. I repelled the ants (not hard to do, they won't crawl through dry powder - a line of flour stopped them) and raised a batch of seedlings successfully.

Last year, I tried again with Strombos, planted July 20. I covered the surface of the medium with finer material (no big chunks sticking up this time) and had it moderately wet, not soggy. I ordered seed from Mesa Garden - nominally 20 seeds, but more than 20 came up. They're not hard to germinate, they're just tiny seedlings that grow slowly. I had a mishap and tipped the pot over, after I resettled it, 13 seedlings were visible. I have had to add water a couple times - I set my sprayer bottle to squirt a stream, open the baggie just a little, and squirt water into the bottom so the pot can take it up from below. I have 6 good strong seedlings, the others are varying degrees of puny - but some of them may make it.