I started coneflowers 1 1/2 months ago and they are not yet ready to transplant. You might want to pick up some mums and cut them back before planting and they will give you plenty of color in the fall.

I don't think you'll get them to bloom that quickly from seed. You would have to buy small plants about 4-5 inches tall at least. I've seen them at nurseries that were that size before.

Coneflowers, daisies, blackeyed susans are not September/October bloomers no matter when they're started.

Aster 'October Skies' and A. tartaricus might grow/bloom in the amount of shade you have.

Tall Sedums like Autumn Joy or Frosty Morn
Dahlias
Asters
Eupatorium

I have started coneflowers from seed and had them bloom in August and September, but you have to time the planting. There is a new variety called 'Prairie Splendor' which blooms in June. I bet if you planted seed now, you could get them to bloom this year. The blooming time of these plants depends on when you sow them. Get some seeds of them and try it. You'll never know unless you try, but I know coneflowers which are planted late often do bloom after your other ones are finished. I've had them blooming right up until frost. One year I sowed an early crop and a late crop. They will bloom at the normal time next year, however.

Here is a link that might be useful: Prairie Splendor

Pineapple sage

Chrysanthemums--hardy mums--will really bloom, usually in October. You can plant small plants now and pinch off any flowers on the plant and any new flower buds until July 15. With a little care the plants will at least double in size and is usually completely loaded with flowers in the fall. I planted a small one last year that someone had in a pot in their home and they gave it to me around July 1--I was not sure the plant still had time to grow, but I pampered it and it bloomed beautiful last year.

Most daylilies would be fine with that amount of sun and they are so low maintenance! You can purchase ones that are mid-late season bloomers or late season bloomers in any colors that you'd like. They won't be from seed, but there are so many sources for them, it shouldn't be hard to find them.

Daisies, echinacea, black-eyed susans are summer bloomers, not fall bloomers. However, if it were me, I'd plant summer bloomers along with the fall bloomers so you'll have something going all the time (one of the hallmarks of a good perennial garden).

For fall blooms:
* Sedum
* Japanese anemone
* Perennial grasses
* Plumbago (groundcover)
* Mums (hardy types)
* Ajania pacifica (gold-and-silver chrysanthemum) - probably the latest bloomer in my zone, gets going in November!

Maximillian Sunflower--perennial. It's very late blooming
but foliage is attractive even if frost comes before bloom.
Reblooming iris. Bog sage which was perennial for me for 5 years until we got -23 degrees one winter. I'm zone 5, it's zone 6. Persicaria Painter's Pallate--mostly for foliage in part shade--has little red blooms in Sept.

Chris