Crop Science Society of America. Weak seedling vigor of native North American perennial bunchgrasses may result in poor establishment-season herbage dry matter (DM) yields (HY). Interseeding North American annual legumes as an N source during grassland restoration, pasture establishment, or bioenergy crop seeding might compound this limitation. Our first objective was to evaluate yellow Indiangrass [Sorghastrum nutans (L.) Nash], switchgrass (Panicum virgatum L.), and little bluestem [Schizachyrium scoparium (Michx.) Nash] first-season HY in the southern Great Plains of North America. This took place in northcentral Texas on a Windthorst fine sandy loam soil with no irrigation or soil amendments. Our second objective was to measure the effects of cross-drilling native North American annual legumes smooth-seeded wild bean [Strophostyles leiosperma (Torr. & Gray) Piper], trailing wild bean [Strophostyles helvula (L.) Elliott], and showy partridge pea [Chamaecrista fasciculata (Michx.) Greene] on bunchgrass first-season HY. In the drier (340 mm) year, legumes failed to establish, while switchgrass produced 2410 and Indiangrass yielded 1980 kg HY ha1 y1. In the year with 687 mm rainfall, legumes had no negative effects (P > 0.05) on grass HY (5490 kg HY ha1 y1 for switchgrass) despite providing up to 49 through 1800 kg HY ha1 y1 (showy partridge-pea with little bluestem; P 0.05 for year by grass legume interactions). Our results indicate that these bunchgrasses produced harvestable HY during their establishment year and that simultaneously seeding annual legumes did not impair native perennial grass establishment while, in 1 yr, making potential N contributions for subsequent stand productivity.