Quick answer: 4 native Washington plants have a recorded bloom range that includes October.
4 species
- California bay laurel Umbellularia californica · 3 states
- Pearly everlasting Anaphalis margaritacea · 18 states
- Scarlet gilia Ipomopsis aggregata · 9 states
- Shrubby cinquefoil Dasiphora fruticosa ssp. floribunda · 15 states