Lynn, it's an annual but does reseed. I pulled that one up from somewhere else and stuck it in that old copper boiler. I call it "The Revenge of the Cosmos".
Sometimes I'd swear it's on the move.
Like this photo below ...
I've fallen in love with the Cosmos this year, but do get the 'Purity Superior' rather than 'Purity' if you want the tall variety. 'Purity' is much shorter. This one can top 4 ft. The tall Cosmos are the ones that have me smitten at the moment.