I am in zone 6 and did use a 'Gritty' mix in my pots and had a lot of problems till I switched to my own compost mix (from my own compost pile) and my sans have doubled their size every year since. Of course there is some sans that need a more draining soil like Sans Hahnii Golden Hahnii. But mostly the big ones can go into a peaty mix. I have some in a clay mix. With 70 and counting species of Sans. they require different conditions. Also what works for some doesn't do so well for others.
Tiffany grew some nice sans in her own clay base soil outside in her yard.
