General consensus is to harvest when they begin to split.
Around here that is around July 4th.
I would bet it will be in that ballpark timeframe for you as well since we have such similiar climates.
I have seed from about 20 pods from last year that are now abot 6 inch tall plants so I hope to see new flowers next spring.
Did you see my earlier posts with pix of all of the La. Irises that bloomed earlier this spring.
I now have about 100 seed pods. Some look like miniature watermelons.
I have some that are about 4.5 inches long.
Tim