Developmental transitions impact ecology and evolution by altering the way plants interact with their environment. Studies of germination and flowering show that developmental timing has significant impacts on plant fitness and performance, but very little attention has been given to the juvenile-to-adult transition: vegetative phase change (VPC). In this study we used 160 diverse genotypes of Arabidopsis thaliana and mutant lines with altered developmental timing to investigate how plants differentially respond to drought across vegetative development. Specifically, we used measures of growth, fitness, and drought physiology to understand how the timing of vegetative phase change, and the phase a plant is in when exposed to drought, impact the plant’s ability to respond to these stressors. Further, we looked for associations between natural variation in the timing of vegetative phase change and climate-of-origin to understand whether this developmental transition contributes to environmental adaptation. Finally, we conducted a genome-wide association study to identify the genetic loci associated with differential response to drought stress, and natural variation in the timing of VPC.             Overall, we found that the timing of vegetative phase change has significant impacts on plant performance in response to drought stress and that the developmental phase of a plant (i.e., juvenile or adult) alters the impacts of drought on plant growth and fitness. We also found significant variation in response to drought among the 160 different genotypes tested. Further, we found significant relationships between the timing of vegetative phase change and climate-of-origin indicating that the timing of this transition may contribute to both adaptation and acclimation in plants. Our study provides further evidence that vegetative phase change results in important physiological shifts in plants that contribute to their success and should not be overlooked.