Tall morningglory is an annual broadleaf vine and a problem weed in many annual and perennial crops in several countries including the United States. A better understanding of the germination biology of tall morningglory would facilitate the development of better control strategies for this weed. Experiments were conducted under greenhouse and laboratory conditions to evaluate the effects of various environmental factors, such as temperature, light, planting depth, pH, osmotic and salt stress, and flooding duration, on the germination of tall morningglory. The results suggested that the optimum day/night temperature range for the germination of tall morningglory was 20/12.5 to 35/25 C and maximum germination (89%) was observed at 30/20 C. Temperature higher and lower than the optimum range significantly reduced germination. Alternate light and dark did not have any adverse effect on the germination of tall morningglory seeds. The germination was 10% at an osmotic stress of −0.3 and −0.4 MPa, and above that, no germination was observed. Tall morningglory showed some tolerance to salt stress. The germination was 40% and 12% at salt concentrations of 50 mM and 200 mM, respectively. Germination was affected by pH levels, and maximum germination occurred at pH 6, whereas above or below that level, germination was significantly reduced. Maximum germination of seeds was 83 and 94% when sown at 0 and 2 cm depth in soil, within a week of sowing; however, germination was significantly reduced to 76% when placed at a depth of 4 cm or deeper. Under no flooding treatment, 87% of seed germinated, but flooding delayed and inhibited the germination of tall morningglory seeds. It is concluded that several environmental factors affected the germination of tall morningglory, and this information could help to predict the spread of tall morningglory in new areas such as Florida.Nomenclature: Tall morningglory, Ipomoea purpurea (L.) Roth, PHBPU.