I think they are sometimes biennial or short lived perennial. I have had a few overwinter, but mostly re-seed, a lot! Watch for fuzzy round leaf volunteers in Spring. I started some from seed about 10 years ago, love them!
@Nyboy , for me, the volunteers start blooming toward the end of June and will bloom until frost if I deadhead them a bit. There are several different varieties/colors.
I was going to answer @Nyboy 's Question with an I dunno! We planted them last weekend after finding large pots of them on sale for $2. Plan to keep seed and if they do not return on their own I will try to start some from seed. Thanks for the info @Lavender2