If you are planting "different" cultivars of iris.....and you don't want them to bet "mixed in a clump"....plant them at least 12" apart ( I always space at least 18', and usually 24"....so I don't have to dig the clump so often), BUT if you want to make an "instant" clump, using multiple rhizomes of the SAME cultivar.....they're saying to use the "triangle method".
