A study was conducted to increase the biomass and deter weed encroachment in establishing eastern gamagrass (Tripsacum dactyloides (L.) L.) forage plantings. Two species mixtures of eastern gamagrass grown on both 15 and 30-inch row spacings with either switchgrass (Panicum virgatum L.) or big bluestem (Andropogon gerardii Vitman) were compared to eastern gamagrass alone. Biomass measurements were conducted once per year at the boot stage (gamagrass) and late vegetative stage (switchgrass and big bluestem) on the third (2005) and fourth (2006) year after establishment. The switchgrass and big bluestem filled in between and within gamagrass rows and in areas with poor gamagrass population increasing overall yields. Weed encroachment was reduced by the utilization of the two species mixes. Forage quality was not adversely affected with the mixtures. In 2005 there was a trend toward increased gamagrass yields for the plots which were in 15-inch rows (1.33 t/ac) compared to the 30-in row (.89 t/ac). The effect due to row spacing was not observed in 2006. In 2005 there was a trend toward lower gamagrass yields from the plots with switchgrass and big bluestem with average yield reduction of 44% compared to the gamagrass monoculture yield. Switchgrass had the highest yield even when grown with the gamagrass with an average across both gamagrass row spacing of 1.73 t/ac compared to .96 t/ac for big bluestem. In 2006 the gamagrass monoculture yield from the 30 in row spacing increased from .89 t/ac in 2005 to 1.28 t/ac in 2006. In 2006 there was a significant yield reduction of the gamagrass (43%) when grown with the switchgrass compared to the gamagrass monoculture. The switchgrass yield declined 55% compared to 2005 for areas with the gamagrass and 19% in areas without the gamagrass.