Most perennials are rated for their zone, so as long as you look at the zones for a particular plant they will survive winter and yes, fall is a good time to plant. I am getting the last of my potted perennials in the ground this weekend. I am in zone 6/7 and black eye susans are one of those hardy ones that are probably good to zone 3 ???? But yes, coreopsis and Black Eye Susans are great to plant now.

Gardenmom, I think I sent you mixed messages here. When I said fall was a good time to plant, I meant not seeds, and yes, you can plant the coreopsis seeds in the ground (direct sow) now, but you will get alot better germination if you winter sow them, than those left to nature that might be eaten by the birds, washed away by rain/snow, and other "dangers" If that makes sense. I think I misunderstood your question here. Some people do direct sow seeds in the fall, things that reseed easily. I never had much luck, but had had great luck wintersowing, that is why I'm singing it's praises.

Last fall I threw evening primrose, larkspur and a few other seeds in my gardens to see if they would germinate and none did. SO personally, I'd rather save my money and seeds, and get the edge that wintersowing (or some even spring sowing) will get me. There are seeds like cleome, gloriosa daisy, etc. that generally reseed...but I sow those in early spring. I know nature itself sows them in the fall when the plants drop seeds. I hope that I have not confused you even more!