I live near Spokane WA.   We have a very different climate than maritime Seattle due to  being east of the Cascade Mountain range and I live at an elevation of about 2,300 ft.

For the past four-six years I have grown a dozen rebloomers as an experiment in our generally short non-frost season.  To provide  you with perspective to our growing season, here are some of my parameters.  (If you aren't interested, fast forward to the next paragraph) My last spring frost tends to be in mid-May however I seldom plant geraniums before Memorial Day just to be sure of their survival.   My SDBs usually begin blooming sometime between mid-to-late April, although this year they began to bloom in May. Some years I have a light frost in late August.   Most years it is in mid-Sept.  This year the first light frost was in mid-October.   Today may be our first geranium-killing frost. 

'Autumn Wine' has been a consistent spring and fall blooming TB iris with and average 2-8 stalks in the fall dependent upon the timing of the first killing frost. Approximately 2-4 stalks per week begin appearing in September, so the more weeks without a killing frost, the more stalks I enjoy.   This is a great time spacing for bringing flowers indoors to enjoy.   The fall flowers can be bunchy, but not always.    It has been my most  consistent rebloomer.   For the past two years I have not fertilized it after the spring bloom so that I could eliminate fertilizer as a rebloom trigger.

'Brother Carl' blooms both spring and fall whenever I have at least 5 months without frost.  'Brother Carl' seems to need a slightly stronger difference in low light to trigger the fall rebloom sequence, e.g., it needs a shorter daylength to trigger rebloom than that needed by 'Autumn Wine'.  So if I only have 3 months without a killing frost, BC won't get a fall reblooming season, but if I have a later frost, I do get a fall bloom season.   This year it produced 8 stalks.   This is my second most consistent iris to rebloom in the fall without any fertilizer application after the spring bloom season.

The other rebloomers that I grow seem to be impacted by fertilizer (they need it to trigger the fall bloom) or the cultivars tend to be inconsistent in the spring if they bloomed the previous fall.