Shoot, nobody from your zone has answered. Have you seen them growing in your area?

Your US zone 4 is the borderline zone. If you have a sunny bed beside a chimney that is where they would have the best chance to winter over (with lots of mulch).

I have seen some growing and blooming last spring here in South Dakota along a foundation. We are zone 5, but we had only -5 F as our lowest temperture last winter, and that wasn't for very long. It was unusually warm. Usually we have a week of lows in the -20's. Also, I don't know how long they have been planted at that location as I am new to this neighborhood, but it is a large clump.

I have had ZERO luck with Dutch iris and I live in Connecticut. What is the trick?

Here we plant them deep(8) and be sure to fertilize with bulb fertilizer. I always plant at least 5 in a hole. When I used to enter arrangements in a show, I always used them instead of TB'S.

I have resorted to growing a few of them indoors! We will see if they can bloom for me in my bedroom.

The rest are outside. 8 inches? That is worth a try if mine again fail me.

The first year I tried them I thought I had done them too deep. They only had small stringy leaves popping up.