Overview of Vernalization

Spring time is always a popular season for just about everyone who cannot wait to see sunny days and warmer temperatures.  Spring is also the time when most plants begin to break out of their winter dormancy and start to leaf out and flower.  It is the spring time show of flowers that is the most dramatic aspect of the season for most.  Thanks to a process known as vernalization, plants know that spring is the time to flower.

Vernalization is the cooling down and adjustment period that all perennial plants must go through in order to bloom when spring arrives.  The word vernalization stems from the word vernus, which is Latin for spring.  This process can be naturally induced by fall and winter or artificially induced in a climate controlled greenhouse.  The gradual decrease in temperatures and the shortening day length signals the plant to stop certain actions such as growing and producing leaves and to begin going dormant.  Vernalization takes place after the plant has gone dormant and the temperatures are low enough to signal the plant’s genes to go into flowering mode as soon as the temperatures warm up upon the arrival of spring. 

If vernalization did not occur, flowering plants would not flower at the right period of time or not at all.  If the plants are subjected to a short winter that still satisfied their vernalization, the plants may break out of dormancy and begin to flower if the temperatures suddenly warm up.  Or, if the winter temperatures never drop low enough for vernalization to occur, the plant may still think it is summer and will not go dormant. 

Plants grown in greenhouses can be tricked into flowering with an artificial vernalization.  As long as the plant is given adequate time to complete its vernalization process, it will flower when it thinks spring has arrived, regardless of the time of year.  Artificial vernalization is not the same as forcing flowers.  Forcing involves taking branches or stems that have buds on them from plants that will bloom at a later time and bringing them into a warmer environment, such as a greenhouse or a home, which will force them to bloom early.  This method is used frequently in the florist industry for floral displays.

Vernalization using cold temperatures is most often seen in temperate zoned plants.  Tropical plants do not go through vernalization in the same way that temperate zoned plants do.  Instead, timing of flowering for tropical plants is signalled by periods of dryness followed by increased amounts of rain and high temperatures.  Plants that are known as annuals do not need a vernalization period in order to flower either.  Because they cannot survive temperatures below 50 degrees F, annuals must flower as soon as they reach maturity.  

Without vernalization, spring would not be the same.  There would be none of the flowers that everyone comes to expect when the days of winter have finally passed.  So, in a sense, vernalization makes winter necessary for spring to occur.