Be sure to save some room between your iris plants and new perennials to put in some bulbs in the fall that will bloom before the iris in spring. Tulips and daffodils, amongst others will be lovely there. They only bloom a short time but then their foliage will be covered up by the iris and other perennials as they come along.
How about some chrysanthemums for flowers in the fall? They have pretty foliage through the summer and a beautiful display just when everything else is winding down.
Could you please complete your personal profile to tell us where in the world you are? Just your climate zone really isn't quite enough info to recommend specific plants. It only tells us how cold it gets on average in the winter there. We need to know how hot, and humid or dry it is, and what your soil is like as well. The more info the better for you to get good answers to your questions.
