[political1]

Why not cross-hybridize pot with kudzu, and then let it grow wild. It would kill the market. Think about it; why buy pot from some dealer when you can just stop on the side of the road and grab some.

[Boogieman]

It already grows wild quite freely in most environments, but the wild plants are worthless for commercial purposes. They must be separated by sex at a certain stage of cultivation, otherwise they will end up with a negligable value as a drug.