In its description of the "Johnny Potseed" poster in its collection, the Hash, Marihuana, & Hemp Museum of Amsterdam-Barcelona notes:

"[The] Johnny Potseed poster (1969) was made by illustrator George Goode and printed with fluorescent ink, so it glows under ultraviolet light. The name Johnny Potseed comes from Johnny Appleseed, a folkloric hero who scattered apple seeds during his journey through the United States. But is Johnny Potseed an urban legend or a real person? In October 1968 the Californian newspaper Times-Standard published an article about a hippie who was scattering cannabis seeds on fertile ground. The agent who chased him across various states gave him the nickname Johnny Potseed. According to police reports, the planter scattered cannabis seeds in abandoned farmland in broad daylight. Then he made maps of his latest cannabis plantings to send to fellow hippies."

Source: https://hashmuseum.com/en/collection/cannabis-counterculture/johnny-potseed/