This paper aimed to determine the effect of different irrigation levels on four varieties of gladiolus (Gladiolus grandifloras L.). The study was carried out in 2016 at the Agricultural Research Station of Canakkale Onsekiz Mart University in Canakkale, Turkey. Four different types of gladiolus (White Prosperity, Peter Pears, Red Balance, Priscilla) were irrigated by the drip irrigation method. We applied four irrigation levels: 100% (control treatment), in which water was refilled in the root zone up to field capacity and 75%, 50% and 25% of the control treatment. In order to understand the water stress and drought resistance mechanisms of the four varieties, thermal images were used in this study. The amount of irrigation water applied changed depending on the variety. Priscilla consumed more water than the others. Leaf temperature of all gladiolus varieties increased with an increase in water stress. In addition, indices calculated from the thermal imaging changed significantly depending on the irrigation water applied to all gladiolus varieties. Priscilla was found to be more sensitive to water stress than other varieties. It is suggested that the use of thermal imaging with regard to both determination of water stress and selection of drought resistant varieties is a useful method.