What is it about Iris that they seem to thrive in the most unlikely circumstances?

Mr. P has an old compost pile that he dismantled a few years ago. These showed up on the edge of it. Unplanted, uncared for but absolutely glorious:

In another corner of the yard, in a place that rarely gets any extra water, or care, this one is blooming right now...

I've put a ribbon around this blue one and when it's time, I may move it closer to the house. This is one of such a limited number of plants that the deer leave alone, I should grow more of them.

I'm still just amazed at how hardy and tenacious they are with so little care.