Quick answer: 21 native Montana plants have a recorded bloom range that includes September.
21 species
- Big bluestem Andropogon gerardii · 25 states
- Black-eyed Susan Rudbeckia hirta · 42 states
- Blue grama Bouteloua gracilis · 15 states
- Buffalograss Bouteloua dactyloides · 9 states
- Common gaillardia (blanketflower) Gaillardia aristata · 11 states
- Common yarrow Achillea millefolium · 31 states
- Cutleaf coneflower Rudbeckia laciniata · 21 states
- Dotted blazing star Liatris punctata · 10 states
- Fireweed Chamerion angustifolium · 28 states
- Harebell Campanula rotundifolia · 25 states
- Indiangrass Sorghastrum nutans · 19 states
- Little bluestem Schizachyrium scoparium · 23 states
- Mexican hat Ratibida columnifera · 17 states
- Pearly everlasting Anaphalis margaritacea · 18 states
- Purple prairie clover Dalea purpurea · 5 states
- Rocky Mountain bee plant Peritoma serrulata · 22 states
- Scarlet gilia Ipomopsis aggregata · 9 states
- Scarlet globemallow Sphaeralcea coccinea · 5 states
- Sideoats grama Bouteloua curtipendula · 25 states
- Swamp milkweed Asclepias incarnata · 25 states
- Switchgrass Panicum virgatum · 24 states