Regarding I. tuberosa -- I planted about 50 of these in Z5 Kansas in 1999. There are still about a dozen in several places that flower each spring at my parents garden. These have experienced lows below -10F. The survivors are planted in heavy clay that dries into brick during the summer. The others were in richer soils. Maybe it is the soil and summer that is the problem and not the winter. Or the soil and winter.
Aaron Floden
now in a better climate, east Tennessee
--- On Fri, 3/12/10, Jim McKenney <jimmckenney@jimmckenney.com> wrote:
Another interesting iris is also beginning to bloom: Iris tuberosa
(Hermodactylus tuberosus). I’ve seen some hardiness claims for this plant
which I now regard as fantastic. I can’t keep it going in the open garden
here in zone 7 Maryland, but it thrives in a cold frame. Has anyone else
been able to establish this plant in the garden in zones 7, 6 or colder?
It’s a really striking flower, well worth a bit of trouble.