Lettuce is the most consumed hardwood crop in the world. Originating in temperate climates, early flowering of lettuce is induced in regions and/or periods of high temperatures. The objective of this work was to evaluate the tolerance to bolting of cultivars of crisp lettuce, during different growing seasons, in the western region of the state of Santa Catarina, Brazil. The experiment was conducted using a randomized complete block design, in a 6 x 2 factorial scheme comprising six cultivars (Milena, Vanda, Vera, Valentina, Pira Verde, and Grand Rapids) and two distinct growing environments (protected and field), during two growing seasons in the summer period. The following were evaluated: days from transplant to flowering, stem length, diameter, total fresh and commercial mass, number of leaves, and commercial and total productivity. Data were submitted to analysis of variance and comparison of means by the Tukey test (p <0.05). The Pira Verde, Milena, Valentina and Vanda cultivars were found to be tolerant to early tillage under the tested conditions. In the protected environment, the best growing season for crisp lettuce was the first summer period evaluated, involving seedling transplant in February and harvest in April. In contrast, the best growing season in the field environment was the second summer period, with seedling transplant in March and harvest in May.