Before flowering, a plant must attain the ripe-to-flower condition. To attain this condition the plant must complete a period of vegetative growth. Attainment of this condition does not automatically lead to the initiation of flower primordial.
Certain environmental condition must follow. Temperature and the duration of light and dark periods within the 24 hour cycle are the two important environmental factors that influence the initiation of flower primordial in a plant that has attained ripe-to-flower condition. The response of a plant to this aspect of light is called photoperiodism.
When appropriate photo period is given to a plant that has attained the ripe-to-flower condition, this metabolism is altered. This results in the formation of flower stimulus, which may be a hormone (florigen).
When this flower stimulus is translocated to the shoot apex, the vegetative shoot apex is transformed to reproductive shoot apex, which results in the initiation of flower primordium.
In natural conditions, the period taken to attain the ripe-to-flower condition and the period taken to obtain appropriate photoperiod differ widely among different plant species. Kurinji (Strobilanthes kunthianus) needs a period of 12 years for having to be subjected to a cycle conducive to flowering.