Quick answer: 9 native Washington plants have a recorded bloom range that includes September.
9 species
- Bunchberry Cornus canadensis · 7 states
- California bay laurel Umbellularia californica · 3 states
- Common gaillardia (blanketflower) Gaillardia aristata · 11 states
- Fireweed Chamerion angustifolium · 28 states
- Harebell Campanula rotundifolia · 25 states
- Pearly everlasting Anaphalis margaritacea · 18 states
- Rocky Mountain bee plant Peritoma serrulata · 22 states
- Scarlet gilia Ipomopsis aggregata · 9 states
- Shrubby cinquefoil Dasiphora fruticosa ssp. floribunda · 15 states