'Grown in Washington': the marijuana farms near US power hub In February 2015, Washington DC joined the list of US states to allow recreational marijuana use, limiting residents to a maximum of 2 ounces and 6 cannabis plants per person. But despite the city's approval, Congress has failed to authorize a bill to set up a market for legal marijuana, a sector professionals say could be worth $22 billion by 2020. A voiced AFPTV report.