Quick answer: 19 native Delaware plants have a recorded bloom range that includes September.
19 species
- Black-eyed Susan Rudbeckia hirta · 42 states
- Blue mistflower Conoclinium coelestinum · 26 states
- Butterflyweed Asclepias tuberosa · 37 states
- Cardinal flower Lobelia cardinalis · 37 states
- Common buttonbush Cephalanthus occidentalis · 23 states
- Common yarrow Achillea millefolium · 31 states
- Dense blazing star Liatris spicata · 15 states
- Devil's walking stick Aralia spinosa · 14 states
- Eastern purple coneflower Echinacea purpurea · 22 states
- Great blue lobelia Lobelia siphilitica · 32 states
- Hollow Joe-pye weed Eutrochium fistulosum · 14 states
- Maypop passionflower Passiflora incarnata · 13 states
- New England aster Symphyotrichum novae-angliae · 18 states
- Scarlet beebalm Monarda didyma · 18 states
- Spotted beebalm Monarda punctata · 14 states
- Swamp milkweed Asclepias incarnata · 25 states
- Swamp sunflower Helianthus angustifolius · 15 states
- Trumpet vine Campsis radicans · 24 states
- Witch-hazel Hamamelis virginiana · 28 states