Green’s Dictionary of Slang

(US campus) fashionable.

1975		J. Roe Same Old Grind 92: [of a hairstyle] ‘Wild, huh? Cosmic, tough, bad, too much— ’ ‘Organic,’ said Thayne .
1977		Eble Campus Sl. Apr. 3: organic – fashionable [...] Wearing Earth shoes is organic.
1996		Eble Sl. and Sociability 63: In the early 1970s when Earth Day was established and environmental concerns were reflected in the dress, food, and music of college students, the term organic meant ‘fashionable’ and carried positive connotations, as in ‘Wearing Earth shoes is organic’.