The innovative cannabis industry conference Hall of Flowers prepares for its Santa Rosa, California, event on September 22 and 23, 2021. It’s the first large-scale, in-person conference for the industry since the pandemic began in 2020. With it, cannabis industry insider attendees can expect outdoor activations, close to 300 exhibitors, and plenty of California cannabis worth showing off. How many people is Hall of Flowers expecting for its redemption song? “3,500 - 4,000 attendees,” says…