An agricultural implement includes a row unit frame (202) coupled to a draw bar (204) by a height-adjustable mount, a set of opening discs (212) coupled to the row unit frame such that the opening discs are vertically fixed relative to the row unit frame, and a biasing member (210) configured to adjust a height of the row unit frame to maintain the opening discs in soil at a selected elevation relative to the draw bar. A method of planting may include determining a height of a draw bar relative to a surface of soil, and adjusting a height of the row unit frame relative to the draw bar to apply a force to push a seed trench opening assembly into the soil and form a trench therein. The height of the row unit frame relative to the draw bar may be independent of the hardness of the soil.