Hear it through the grapevine

To learn information through informal channels, gossip, or unofficial sources rather than through direct or official communication.

This phrase originated during the American Civil War in the 1860s, referring to the 'grapevine telegraph' - a derogatory term for unreliable information networks. The comparison to grapevines emphasized how rumors twisted and turned as they passed from person to person, like the winding growth pattern of grape vines.