ABSTRACTIntercropping corn (Zea mays L.) with forages, such as palisadegrass {Urochloa brizantha (Hochst. ex A. Rich.) R. D. Webster [syn. Brachiaria brizantha (Hochst. ex A. Rich.) Stapf]} or guineagrass [Megathyrsus maximus (Jacq.) B. K. Simon & S. W. L. Jacobs (syn. Panicum maximum Jacq.)], provides large amounts of biomass for use as straw in no‐tillage systems or as pasture. However, it is important to evaluate what time these forages have to be sown into corn systems to avoid reductions in both corn and forage production. This study, conducted for three growing seasons at Botucatu, Brazil, evaluated nutrient concentration and yield of corn as affected by time of forage intercropped as well as forage's dry matter production. Our data showed that intercropping systems did not reduce leaf nutrient concentrations and grain yield of corn in relation to sole corn. The simultaneous intercropping of corn and guineagrass resulted in the lowest plant population (51,200 plant ha−1), number of ears per plant (1.0), and, consequently, the lowest corn grain yield (9801 kg ha−1). Guineagrass seeded at the time of corn fertilizer topdressing resulted in the highest plant population (59,400 plants ha−1), number of ears per plant (1.2), and corn grain yield (12,077 kg ha−1). Forage production was highest when intercrop was done simultaneously. Palisadegrass could be intercropped with corn both simultaneously or at topdressing fertilization stage. In contrast, it is recommended that guineagrass should only be intercropped with corn at topdressing fertilization.