When you plant cool flowers depends on first and last frost dates. Whether or not a flower should be planted in fall or spring is dependent on hardiness zone. If a flower is hardy in your zone, it should be planted in the fall. If a flower is not hardy in your zone it should be planted in very early spring. Lots more information on the how, when, and why in this video – https://www.youtube.com/watch?time_continue=2&v=YPZpLBFOfh0&feature=emb_logo
Here is how I do things in 6b with a first frost of Oct 21 and last frost of April 15th
Directly sown in the fall 6-8 weeks before the first frost –
Larkspur, Bachelors Buttons, Orlaya, Nigella, Bells of Ireland (did not grow this year but works well)
Transplant started inside and planted out in the fall 6-8 weeks before the first frost-
Dara, Sweet William
Directly sown in early spring 6-8 weeks before the last frost –
Cerinthe, Bupleurum, Corn Cockle, Saponaria, Sweet Peas, Starflower, Poppies
Transplants planting out in early spring 6-8 weeks before the last frost –
Snapdragons, Scabiosa, Ammi, Lambada, Foxglove, Feverfew (have tried in fall – usually lose them to moisture), Lisianthus (I’m sorry I forgot to show this. It is currently budded up), Strawflower
There are additional cool flowers, but these are the ones I’m growing this year.