Growth and compositional changes in a forage sward are complex. This study analyzed the changes as growth occurs in alfalfa (Medicago sativa L.)-reed canarygrass (Phalaris arundinacea L.), and alfalfa-orchardgrass (Dactylis glomerata L.) mixtures. Monocultures and mixtures (one row of grass between two rows of alfalfa or one row of alfalfa between two rows of grass) were sampled at five, 10-day intervals during spring and summer growth for two years;Alfalfa-grass mixtures outyielded alfalfa monocultures during only one (spring) of the four growth periods sampled. The yield potential of alfalfa in binary mixtures adjusted to an equal-area-basis was increased 15 to 66% over monoculture yields. On this basis, as the distance between alfalfa rows increased, the yield potential also increased;Alfalfa and alfalfa-grass in vitro digestible dry matter (IVDDM) and nitrogen (N) concentrations were higher, but cell wall (CW) concentrations were lower than grass monocultures. Alfalfa IVDDM, CW, and N concentrations of alfalfa in binary mixtures were not affected by grass association;Alfalfa was stratified into component parts consisting of tops (above 30-cm) and bottoms (below 30-cm). The leaf-to-stem (L:S) ratios of alfalfa bottoms were not affected by grass association, but the L:S ratios of alfalfa tops were significantly increased (p < 0.05). Digestibility and chemical composition of alfalfa leaf and stem components were not affected by grass association. Large compositional differences between stem tops and bottoms were observed but not for leaves;Grass yields in binary mixtures were not significantly increased by alfalfa association. The N concentration of grasses next to a single row of alfalfa increased 11%; grass between two rows of alfalfa increased 20% as compared to monocultures. The IVDDM concentration was higher (p < 0.01) and the CW concentration lower (p < 0.01) in reed canarygrass associated with alfalfa as compared to monoculture. Although not significant, similar trends were observed for orchardgrass.