Arnold, Iris cristata grows quite well for me here in Ottawa which is
Zone 4B. I know it also grows in Chalk River, which is Zone 3, or very
close. I found that it took a little effort to get it started but now
it is quite happy in a shady and a sunny spot.
The same comments apply to I.lacustris which I have recently obtained
from a woman in Chalk River through a friend. I do not know this woman
but, I am told, that she has been growning I.lacustris for decades and
they cover an extensive area of her garden.
Ian, in Ottawa