Apple rootstock M.9-T337 was studied to see how it handles drought. As drought stress increased, the water content in the leaves and soil decreased. The leaves became more water-efficient at first, but then less efficient after 20 days of drought. The plants' ability to photosynthesize decreased gradually with drought. Infrared imaging showed temperature differences between stressed and unstressed plants after 15 days of drought. When the plants were irreversibly damaged by drought, specific values for water stress were reached. A standard for grading drought stress was created, and it was determined that the best time to water the plants is when they reach grade 3.