The Wolverines (8-3, 6-1 Big Ten) weren't stopped on offense by the hapless Hawkeyes (4-7, 2-5) until Gardner threw an interception early in the fourth quarter.
Gardner threw three touchdowns and ran for three scores. He became the first Michigan quarterback to account for six TDs since 1983 when Steve Smith had as many passing and rushing scores in a game at Minnesota.
Denard Robinson played after missing two-plus games with nerve damage in his right elbow. Robinson started at running back and took some snaps at QB, but didn't throw a pass.
Michigan running back Fitzgerald Toussaint appeared to break his left leg on his team's first drive.
The Associated Press contributed to this article.