The growing demand for organic products and the need to plant onions (Allium cepa L.) in the town of Pinhais, Brazil at different times of the year generated this study in the Organic Horticulture Experimental Station of Canguiri-Federal University of Parana, Pinhais, Brazil. The objective was to evaluate the agronomic performance of seven cultivars of open-pollinated onion in an organic system in two planting seasons (January and September) different than traditional times (April and June). The experimental design was completely randomized in a 7x2 factorial scheme with three replicates: Franciscana IPA-10, Vale Ouro IPA-11, Brisa IPA-12, Alfa São Francisco (Cycle VIII), Alfa São Francisco -RT (Thrips tabaci-resistant genotype assessment - Embrapa Semiarid) and BR-29. The results were evaluated for homogeneity by Bartlett’s test and treatment means were compared by Tukey’s test at a significance level of 5%. The variables assessed at the start of bulb formation and harvest were stem height, fresh and dry leaf weight, leaf number and scape diameter. At harvest we measured dry and fresh mass of the bulb, bulb type according to the diameter and productivity. The cultivars Alfa São Francisco and Alfa São Francisco-RT produced higher values of dry mass and productivity in January.