Photoperiodism is the way an organism responds to the changes in the length of the day. A biennial plant is a flowering plant that takes 2 years to complete its biological cycle. After the first year, they usually enter the period of dormancy. During this period they are subjected to cold treatment or vernalization to accelerate flowering and shorten the vegetative phase of the plants. When plants are subjected to low temperature, vernalization promotes flowering by a period of low temperature it stimulates a subsequent photoperiodic flowering response.