I've grown Iris cretensis (aka: Iris unguiculares ssp cretensis) in the ground in southwestern Ohio for about 9 years. It has dwindled recently due to competition from other perennials, but it's delightful when it's warm enough to bloom on Christmas Day and New Years day. No other iris I've grown comes close to blooming that time of year. The big flush comes in March. Bill Shearer of Virginia taught me it was cold hardy about 10 years ago, and I've been delighted ever since. I should note that my clumps are within a few feet of the house... so they are getting some added protection from that. Dennis in Cincy (Zone 6-ish)