Stress memory is an adaptive strategy evolved by plants that enables them to anticipate and survive stress events in a fluctuating environment. One of the most well-studied forms of stress memory in plants is thermomemory, in which exposure to moderate heat stress primes the plants, allowing them to survive subsequent, otherwise lethal, and severe temperatures. However, despite significant progress, our current understanding of heat stress memory in plants is still not complete, particularly regarding the understanding of how this priming and memory are controlled at the molecular level. We therefore provide a detailed protocol for the thermomemory assay, as well as information on how to validate the thermomemory phenotype at both the physiological and molecular levels.