Celery is appreciated for its nutritional value. “Commercial maturity” is established by the size of the plant; however, the antioxidant content has an effect on the nutritional quality and should be considered when defining the time of harvest. The objective was to characterize the antioxidant compounds present in celery stalks in three zones (outer, middle and inner) at different stages of development, to recommend the harvest-time that maximizes nutritional quality. Ascorbic acid (AA) and total phenolic compounds, such as browning potential (PP) and quinones (QT) were meassured. The AA and PP decreased with ripening, following a linear trend in all three areas. The AA and PP were higher in the inner zone, while higher QT was observed in the inner and outer zones, remaining constant with ripening. From a nutritional standpoint, the inner zone is rich in antioxidants, but more prone to damage by changes in color. Zonification could affect the taste, astringency and hardness of each zone, considering the elaboration of minimally processed stalks. Celery plants should be harvested before week 3 (94 days post-transplant) to maintain the nutritional value but considering the potential increase in browning.