I transplanted Iris' 4 years ago. Got blooms the first year and none since. Beautiful foliage and has spread.

sounds like too much nitrogen and not enough phosphorous. If you have been fertilizing them try feeding some bonemeal or other high phosphorous. That is the second number on the fertilizer bag. Like 5-10-10. The numbers are Nitrogen, phosphorous and potium in that order, given in percent of total weight. Aslo if they have become too crowded it might be time to thin them. Used to thin mine every other year but crowding usually results in smaller flowers instead of no flowers.