Sorry Unpro, I am of no help what-so-ever, but hope you get some answers soon, as I too am interested.
BA

I don't know about growing them from seed, I would think any seed-growing info you can find in posts about any spiny terrestrials on the forum would work. Anything like Dykia, Hetchia, Deuterocohnia, etc. I have my Puyas growing in the ground and in pots...the ones in pots range from slightly more sandy potting mix to just whatever I use on any other plant. Sorry not to be any more helpful or specific for you. Are you planning on growing them outside, potted, in a greenhouse for the winter?

That is helpful. :)

Would be outside during the summer, and in a heated greenhouse during the winter.

Good to be of any help. Good luck. Let us know how it goes (pictures always help!).

Hi. If you are growing them in pots you will need to think about how big they will eventually grow and how you will move them into the greenhouse for winter! Sp like chilensis, berteroniana, alpestris grow very large (over a metre across) and are ferociously spiny. Mine are in pots now but I plan to plant them out in a sheltered spot once they have got to a reasonable size. I use a 50-50 mix of soil based compost and sharp grit.
Cheers
Ali

Good point! Who wants to be handling spikey pots?
BA