I have a lot of irises clumped together -they need dividing and also sun. The area they are growing has no sun, only one has ever flowered and it's very pretty! I can wait to move them, there is no rush. When would be the perfect time to move them? I want to put them in front of the lilacs I just moved.
I divide and/or move mine in October. Then they have plenty of time to settle in and be ready to bloom in the spring. What passes for winter here doesn't arrive until sometime between Halloween and Valentine's day but if you get real winter you should adjust that timing accordingly...maybe mid-late Sept for you?