Three polyethylene mulches (black, white and gray) and two planting systems (direct seeded and transplant) were tested in common onion (Allium cepa L.) hybrid Yellow Granex PRR, whit the objective of evaluating the duration of developmental stages. The phenophases established were: Emergence, first true leaf, young plantlet, bulb filling initiation, maximal vegetative development and bulb filling termination. There were differences among planting systems in the duration of phenophases; the least duration occurred with the black and gray polyethylene mulches. The combination of these colored plastics and direct seeding shortened the vegetative cycle in 70 days and the yield per plant was higher than in the white plastic mulch and bare soil.