Well, they sell the seeds for both Sonata mix, Sonata pink and Sonata blush (and white, of course), so it's pretty safe to assume they aren't going to be sterile. I know it's a bit hard to imagine, as they seem to self-seed so easily, but cosmos are generally considered to have a low germination rate. But still, none at all is pretty rotten odds. Might you have inadvertantly weeded out what seedlings did manage to germinate?

I was thinking that because they sold the seed it shouldn't be sterile, too. I don't remember weeding at all :-( but you're probably right. Either that or the squirrels like them.

I had the same thing happen - not one single seed germinated. I didn't weed or destroy the seedlings - they just did not come up. I was amazed as I have had no problem with cosmos before. I will see what happens this year - bought seeds last year. Maybe they have started producing terminater seeds already.