Flowers tend not to own calendars, so how do they know when to bloom?

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Sources:
http://www.livescience.com/32529-how-do-flowers-know-when-to-bloom.html
http://www.washington.edu/news/2012/05/25/its-in-the-genes-research-pinpoints-how-plants-know-when-to-flower/
https://www.mpg.de/7530520/flowering-time-arabidopsis
https://www.nsf.gov/pubs/2002/bio0202/model.htm
https://www.britannica.com/science/meristem
http://www.livescience.com/377-mystery-solved-plants-flower.html
http://science.sciencemag.org/content/309/5741/1694.full