The product Grass B Gon can take care of your quack grass problem without affecting the irises or peonies or daylilies. I could not garden here without it. It works best when sprayed on while it's actively growing. It takes a while to kill it, but it will die.
The shorter the growing season, the less likely an iris will bloom the year after transplanted. Often taking a couple years.
You might have better luck growing the intermediates and MDB's in your zone. They tend to do better in colder climates.
Good Luck!
