My snapdragons come back every year Why?

Question

I've been growing snapdragons for years, and they come back every year different colors shapes and sizes i've read that they don't come  back mine do so do my Petunias, why is this? Am I just an awesome grower or is there a reason although I do not pull them at the end of the year I Let them die and they just come back My neighbor also now has snapdragons,petunias,asylum which i plant I understand it's the insects that carries the seeds  all but the asylum I don't understand  why the come back,

why is this? Can you give me some info on my question?

Answer 1

I never pull them out when they die off....somehow some seeds drop from the flowers pinched and they reseed in the spring.