The nice thing about companion plants for irises in this zone is bloom time goes from late February when you can plant the bulbous irises among a sea of grape hyacinths or crocus to the late blooming TB's in early June to catch the first of the early roses. I put creeping or moss phlox along the edges of the iris beds. The phlox makes a tight groundcover that I keep away from the rhizomes and the bloom colors ranging from white/pinks/lavenders go very well with brighter shades of dwarf irises.
