Stoffyn, O. M., Tsao, R., Liu, R. and Wolyn, D. J. 2012. The effects of environment and storage on rutin concentration in two asparagus cultivars grown in southern Ontario. Can. J. Plant Sci. 92: 901-912. Flavonoids have been shown to have many human health benefits due to their antioxidant activity. Concentration of rutin, the primary antioxidant in asparagus spears, can vary significantly with cultivar, location and season. Assessment of rutin in cultivars across locations throughout the harvest season in Southern Ontario, as well as in stored asparagus, is important for defining the potential benefits of consuming local asparagus. The objectives of this research were to determine the effects of cultivar, harvest time, location, spear diameter and part, and storage of fresh spears and freeze-dried flour on rutin concentration. Sampling date over the 6-wk harvest season and location did not significantly affect rutin concentration in either of the two cultivars tested. Rutin concentration was inversely related to air temperature before harvest and spear diameter, and for any given diameter, was highest in the tops of spears and decreased towards the bottom, in both cultivars. Soil temperatures before harvest were not correlated with rutin concentrations. Storage of fresh spears at 4°C, or freeze-dried flour at varying temperatures, did not affect concentration. The stability of rutin concentration throughout the harvest season, across locations and in stored products suggests predictable antioxidant levels in Ontario-grown asparagus.