Limited photosynthetically active radiation (PAR) can reduce interseeded cover crop growth in corn (Zea mays L.). Two experiments in North Dakota evaluated the effect that hybrid relative maturity (RM), row width, and cover crop planting date have on cereal rye (Secale cereale L.) and winter camelina [Camelina sativa (L.) Crantz.] establishment when interseeded into 80 and 89 RM hybrids at V7 and R4 growth stages in 56- and 76 cm corn row widths. Cover crop biomass was typically less than 100 kg ha-1. In the following spring larger amounts of PAR beneath the 80 RM hybrid increased cover crop biomass by 20.8 kg ha-1. Cover crop biomass tended to be greater in the 76 cm row width but was not significantly different from the 56 cm width. Cover crops decreased residual soil nitrate by 6.0 kg ha-1 in the fall and by 15.6 kg ha-1 in the spring.