Abstract: A mulching rotary lawn mower that cuts and returns grass clippings to a lawn wherein the proportion of grass clippings that are finely cut by the rotating cutter blade can be selectively increased or decreased by provision of a collection chamber at the rear of the housing containing the rotating cutter blade, the collection chamber having a mulcher plate with a plurality of openings which can be pivoted from a substantially vertical position wherein the plate is tangential to the circle described by the cutting tips of the blade or moved rearwardly about a 45.degree. angle, thus effectively enlarging the collection chamber while closing the openings therein, so that a greater proportion of the grass clippings cut by the blade are received in the collection chamber, but which clippings, on the average, have been cut a lesser number of times and therefore are coarser than when the plate is in the vertical position. The position of the mulching plate is controlled by a handle readily available to the operator.