Marijuana is known for the psychoactive ingredient known as THC, but do people know where THC is produced? This substance actually comes from the flowers or buds of the marijuana plants. Marijuana plants begin to flower when they reach a particular height, usually at least six inches, and have grown around five sets of leaves.  Generally, marijuana gardens are composed of male and females plants. The male marijuana plants also are able to produce flowers that look like playing card clubs. ...