Best way to propogate Hollyhocks?

Hi everyone, I was wondering what the best way would be to get my Hollyhocks to keep growing year after year? Do you let them naturally reseed themselves (letting the seeds drop and overwinter on the ground) or do you gather them up and spread the seeds in the spring at planting time? Is there some advantage to those seeds being on the ground all winter? The few times I've tried to let seeds naturally reseed I didn't think it worked as well as it could -- in fact, it was sort of a miserable failure. What plants did grow didn't grow where I wanted them to. Of course, right?
I'm new to this area and for the first time I am experiencing winters that get down to temps like -17 F so perhaps that is too cold for successful reseeding? I think that I'm in a Zone 5 or 6 (I'm sort of on a border here in west central Indiana) and I can't quite figure out how to make this work.
Thanks for any help, Giselle
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