A swath roller apparatus is adapted to be attached to a swather, where the swather is operative to cut standing crop plants and lay cut plants in a swath as the swather moves along the ground in an operating travel direction. A drum is rotatably attached to an axle that is adapted to be movably attached to a rear portion of the swather such that the axle is oriented substantially horizontally and perpendicular to the operating travel direction, and such that the drum moves up and down and rolls along a top of the swath exerting a downward anchoring force on the swath. A bias element is operative to exert a bias force on the axle, and a bias force control is operative to vary the bias force to vary the anchoring force.