I am interested in Dutch Irises too. I tried them for several years. They bloomed once. The issue might be their dormant period; that is, the bulbs are available in spring only. However, they don't wake up in spring, but later, in late summer or even fall. Of course, the winter kills them because they don't go dormant when they ate supposed to go dormant in Zone 5b.
I would appreciate some guidance. Thank you