A disc hub assembly includes a shouldered spindle that is secured to a disc opener frame and to which a depth adjustment arm and a gauge wheel arm are connected. The disc hub, to which a ground opener disc is mounted, is disposed on the spindle in a manner that allows the disc to rotate around the spindle. A gauge wheel is connected to the gauge wheel arm. When the depth adjustment arm is rotated between depth setting positions the gauge wheel arm is also rotated. As the gauge wheel is connected to the gauge wheel arm, rotation of the gauge wheel arm causes rotation of the gauge wheel. The depth adjustment arm is spring biased into engagement with an arc of notches on the disc opener frame. The notches define a range of positions at which the depth adjustment arm may be positioned.