For some flower-colour in fall, we've depended on perennial asters for years, especially New England asters (notably 'Alma Pötschke' (magenta) and short 'Purple Dome') and a smooth asters, 'Bluebird' (powdery blue) (see the three in picture below: October 6, 2016). We've used several hardy perennial mums (bloom a bit earlier) but, overall, the asters are more showy.
New England asters are prominent among the fall-blooming wild flowers here, though we've used garden seleections which are likely much better behaved in a garden than the seeding and running wild types.
Here, our fall asters are good for a month or more of colour (most of September into October). Several need staking and drought will reduce the bloom time. Have used some really nice perennial aster fillers too, notably calico aster and white wood aster. Re formal names: none of our asters mentioned are still formally included in the Genus Aster but have been reclassified.
A taller New England aster along with variegated-leaf phlox 'Nora Leigh' (latter, unlike any other tall phlox we've had, is an exceptional fall perennial, at least here). Picture September 16, 2017.
