North Carolina wants to know if marijuana could one day replace tobacco as a cash crop. Louisiana is wondering how pot holds up in high humidity. And Washington state has questions about water supplies for weed. Colorado agriculture officials this week briefed officials from about a dozen states — some that have legalized weed, others that joked their states will legalize pot "when hell freezes over" — on the basics of marijuana farming and swapped stories about regulating a crop that the federal government still considers illegal. The Colorado Department of Agriculture also is working on the world's first government-produced guidelines on growing marijuana. There's no shortage of how-to books catering to pot growers both in and out of the black market, but Colorado's forthcoming guidebook aims to apply established agronomy practices to the production of marijuana. "When you start with no knowledge at all, it's rough," said Mitch Yergert, head of Colorado's Division of Plant Industry, an agency within the Agriculture Department that regulates marijuana production.