Green manures are an important source of N and organic matter in organic systems. In rotations with small grains, underseeding legumes into stands of winter cereals lengthens their growing period while minimally interfering with cereal growth. We tested the performance of red clover (Trifolium pretense) and white clover (Trifolium repens), underseeded into winter wheat (Triticum aestivum), on establishment, dry matter production and impacts on subsequent corn (Zea mays) yields in Eastern Nebraska. Red clover (RC) and white clover (WC) were grown in 2011, 2012, and 2013. Seeding rates were 22.4 kg ha^-1for RC and 13.5 kg ha^-1 for WC. All seed was frostseeded in March by broadcasting. The legumes were terminated either in November or April. Germination counts were taken in May and whole plant biomass samples were taken at wheat harvest, in October and in April. Corn yields were obtained at harvest. RC germination rates were 48% in 2011 and 30% in 2012 and WC germination rates were 20% in 2011 and 11% in 2012. In 2011, RC dry weight was 4248 kg ha^-1 in October and 4469 kg ha^-1 in April. WC dry weight was 1840 kg ha^-1 in October and 2326 kg ha^-1 in April. Drought conditions in 2012 caused low clover dry weight in October (506 kg ha^-1 for RC and 88 kg ha^-1 for WC). In 2012, the lowest corn yields occurred after spring-terminated RC (1736 kg ha^-1), and the highest corn yields occurred after control treatments (9867 kg ha^-1). We conclude that red and white clover can be established by frostseeding and can have good dry weight production in Eastern Nebraska when precipitation is average. RC should be terminated in the fall before planting corn to avoid large soil moisture deficits.