For what it's worth, mixing sand into heavy clay soil gives you two of the basic ingredients of concrete. All you need to do then is add water, and you're all set (literally!).
We have clay soils here. Irises will grow OK in straight clay, but they perform better with heavy amendments of organic matter. One of the things I've learned about gardening in clay is that tillage is something to be avoided. When creating a new bed, I just spread a 2 - 3 inch layer of coarse compost across the area and plant into that. The compost drains quickly, but it also acts almost like mulch in keeping the soil underneath moist. So the rhizomes stay relatively dry, but the roots have access to moisture.
