The effects of two start irrigation times (250 and 1100 corn heat units (CHU) accumulated after transplanting), two end irrigation times (1700 and 2500 CHU accumulated after transplanting) and two minimum soil moisture conditions (9% and 5% volumetric soil moisture) on flue-cured tobacco (Nicotiana tabacum L. cv. Delgold) grown in southwestern Ontario were investigated over five years in a field study. Early season irrigation, at 9% minimum soil moisture content, starting when 250 CHU had been accumulated after transplanting (9 to 15 days) increased leaf number and yield in one year, quality in two years, and reducing sugars concentration in three years and decreased alkaloid concentration in three years. Irrigation during harvest continuing until 2500 CHU had been accumulated after transplanting (102 to 116 days) did not produce any consistent response. Irrigation at a minimum of 9% vs. 5% volumetric soil moisture consistently increased tobacco growth, yield, quality, and reducing sugar concentration and reduced total alkaloid concentration. The reduction in total alkaloid concentration was attributed to dilution by increased yield rather than a change in the amount of alkaloids produced.