I lost most of my stock of I vartanii at around minus 15 c, the rest died at minus 18 the following winter. The biggest problem growing it is, (in common with some other reticulate Iris in the UK), it does not like temperature/ moisture fluctuations while in full growth. In my experience it doesn't care for freezing temperatures either -even though it may survive. The worst thing for a reticulate Iris is when it gets warm and wet as the leaves start to wither and the roots are dieing off for the summer. I expect it would perform better in a continental climate! Peter (UK) On Thu, Jan 31, 2013 at 5:56 PM, Sean Zera <zera@umich.edu> wrote: > So far I attribute it to luck and abnormally mild winters. I did > temporarily mulch it with leaves the other week, not expecting the emerged > bud to care for below-zero F temps with no snow cover. I'm not sure that > I'll ever be able to get a nice looking flower out of it unprotected, even > if the plant proves completely hardy. > > Sean Z > Zone 6a > SE Michigan > >