Blueberry fruits from five commercial cultivars and 13 breeding selections grown at the same locations over two growing seasons were analysed for total phenolics (TPH), total anthocyanins (ACY), total hydroxycinnamic acids (HCA), total flavonols (FLA), fruit weight and oxygen radical-absorbing capacity (ORAC). Variation in ORAC, TPH, ACY, HCA, FLA and fruit weight among genotypes was much greater than that observed between growing seasons, indicating that genetics plays a more important role than growing season in influencing ORAC and phenolic content in blueberries. Significant main effects for growing season and genotype growing season observed for ORAC, ACY, HCA and fruit weight demonstrate that environmental growing conditions can impact levels of phenolics and ORAC in blueberries and that certain genotypes vary in their capacity to synthesise phenolics under different growing conditions. In general, genotypes with smaller berries had higher ORAC values and levels of TPH, ACY, HCA and FLA than large-berried genotypes. Over both growing seasons, ORAC correlated highly with TPH, ACY, HCA and FLA, while fruit weight correlated inversely with all phenolics measured. Our results indicate that blueberry genotypes should be screened over multiple growing seasons in order to identify antioxidant- and phenolic-rich germplasm.