I pretty much do the same as Lucy.....I just put them where they 'fit" !! I don't like to put the same colors next to each other(i.e. don't plant two white iris next to one another), and like to interspace 'lights" and "darks". I'm usually more concerned on getting the taller iris to the "back" of the bed (the center, in my case), and work progressively shorter as I move to the front.
