Wendy,
Verbena Bonarensis will self sow as well, and of course sun flowers come up everywhere here in my zone 5. Ageratum does as well. HOw do you deal with weeding in the situation of self sowing? That's the main reason I don't do it, my rows get tilled under in the fall and I just start over with transplants, otherwise I can't control weeds.
Cheryl