You may need to further define your "deep shade". Exactly how deep is it? Nicotiana and Actaea simplex both handle a fair amount of shade but they do bloom at the same time (now).

tj

When you specify "tall, flowering" how tall are you aiming at? Toad lily/Tricyrtis hirta grows to 3 ft. tall and blooms here in southern New England (z6a) end of September/ beginning of October every year, is zero maintenance, doesn't spread, not bothered by predators and helps sustain pollinators.

ianna, can you add a photo or give an idea of how much space and light (even reflected light) the area gets? Only shaded from the two side or overhanging branches or . . .?