I find that irises expand quite fast when they get established. I planted bulbs and irises in a south-facing flowerbed along the side of my garage. The pic, taken in 2007, shows yellow Tulip batalini, purple Iris pumila, with Muscari and a bearded Iris beyond them. It only took a couple of years for the irises to start growing over the top of the bulbs. Fortunately, it's quite easy to remove iris rhizomes, as they are shallow-rooted.
