“During the the American Civil War, a Colonel Bee set up a crude telegraph line between Placerville and Virginia City by stringing wires from trees,” according to the Little Book of Answers.
The wires hung in loops like wild grapevines, and so the system was called “Grapevine Telegraph” or simply “the grapevine.”
By the time war news came through the wires it was often outdated, misleading, or false, and the expression “I heard it through the grapevine” soon came to describe any information obtained through gossip or rumor that was likely unreliable, according the Little Book of Answers.