Dear Mary-Sue, for Nivenia I cannot help. But maybe for Aristea. I remember your garden well and I think the Aristea do not like the competition from the redwood roots. And I think it gets too dry for them in summer. I remember many big clumps of Aristea when I was in South Africa, they mostly grew in a meadow like setting with moist fertile soil, some also grew in semi shade in between trees but still moist. I have never tried them in pots, actually never at all so this is all I can tell. But maybe they do well in pots kept moist at the growing season? And I guess they like fertilizer as well. Greetings from Germany..... still freezing cold..... Uli