You are talking about making a self-seeding patch. First you must determine whether cannabis seeds will be killed by the winter cold in your area, which as I recall is more frigid than the stony gaze of a certain stern Secretary of State...
Look to commercial outdoor strains from the far north, ones with fat seeds and tough husks. If you are really serious about this as a long-term project, getting seeds from feral industrial hemp from a cold midwestern state and breeding a drug grade strain into it might be an option. And consider mulching your area very heavily each fall with a thick layer of leaf litter or hay.

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"Careful what you carry- 'cause the Man is wise- you are still an outlaw in their eyes" -Steely Dan
"Multiple pieces of anecdotal evidence do not equal scientific fact." -Rhizome
"If the Queen Bee ain't happy... the hive isn't happy!"-Dutch Pimp
http://boards.cannabis.com/basic-gro...e-harvest.html<-It's a grow guide! Enjoy!
http://boards.cannabis.com/plant-pro...hy-how-do.html <- all the boring stuff about soil chemistry you never wanted to know
http://boards.cannabis.com/grow-log/...ml#post1837597 <-how to make canna caramels
http://boards.cannabis.com/grow-log/...ml#post1820481 <-illustrated cloning guide permalink
Contacting Her Dankness: stinkyattic at hushm4il-please use the same discretion you do on the boards, thanks.
I don't claim to know the first thing about growing anything; hell, I can't make a Chia pet sprout.