Vernalization (from Latin: vernus, of the spring) is the acquisition of a plant's ability to flower or germinate in the spring by exposure to the prolonged cold of winter.
Many temperate plants have a vernalization requirement and must experience a period of low winter temperature to initiate or accelerate the flowering process, or, as the case with many fruit tree species, to actually break dormancy, prior to flowering. Many plant species, including some ecotypes of Arabidopsis thaliana and winter cereals such as wheat, must go through a prolonged period of cold before flowering occurs. This ensures that reproductive development and seed production occurs at the optimum environmentally favorable time, normally following the passing of winter. The needed cold is often expressed in chill hours.
Following vernalization, plants have acquired the competence to flower, although they may require additional seasonal cues or weeks of growth before they will actually flower. One of the most important influences that temperature has on the floral transition is the vernalization response. Vernalization activates a plant hormone called florigen present in the leaves which induces flowering at the end of the chilling treatment. Some plant species do not flower without vernalization. Many biennial species have a vernalization period, which can vary in period and temperature. Typical vernalization temperatures are between 5 and 10 degrees Celsius (40 and 50 degrees Fahrenheit).
In the much studied model species A. thaliana, the apical meristem, must be vernalized in order to promote flowering. Vernalization of the meristem appears to confer competence to respond to floral inductive signals on the meristem. A vernalized meristem retains competence for as long as 300 days in the absence of an inductive signal. It is possible to de-vernalize a plant by exposure to high temperatures subsequent to vernalization.