This is a question that I get to answer every year. Most people either forget or want to forget the answer, because it is not the most pretty of answers. “When to cut back the foliage of an Iris or Peony?”
Well let’s talk for a minute about what is going on with the bulb. The bulbs have put off roots into the soil and when it warmed up in the spring, new growth emerged from the ground and created the foliage and hopefully the bloom. That bulb likes having the cold rejuvenation time during the winter. It also likes to be fed with fertilizer and as much natural stuff as it can.
So that brings us back to the question when can I cut them back? After they have bloomed in the spring, they leave us with some nice foliage for a month or two, then the heat of the summer comes around and the foliage starts turning crazy colors and then to a brown color. The answer to the question is, wait as long as you can stand to look at the dead looking foliage. The longer you let the sap run out of the foliage back into the bulb, the stronger the bulb and the more bloom you will receive next season. The Iris bulbs of course love to be exposed to the sun light, so make sure you are keeping trash and debris off of the actual rhizome bulb through the year and especially the fall during leaf season. Once the Peony leaves are brown, cut them to the ground and forget about them till next year.