Fall.

Is there a reason Fall is best?
I would think I would get rooting and establishment in a pot if I did it sooner.

Hi Judy, the Pacific coast iris can only be divided when they are actively growing. You will see white shoots coming off the roots. They are only actively growing in the spring and fall. I think late September or early October is the best time to divide Pacific coast iris. I have been told if you divide them when they are dormant in the summer they will die. I've never tried it myself. Karen

flowerfan is correct - PC iris are a bit fussy about root disturbance at the incorrect time of year. Fall is really ideal for dividing or transplanting of these. In general, fall division is recommended for spring/early summer blooming perennials and early spring for later blooming perennials.

Having said that, I've divided Sibes at all different times of the year with good success, however they often miss a season of bloom if I did it at any time other than early fall.