Why Do Onions Vary in Flavor & Storage Time?

In our onion video Tricia discusses choosing onions to fit your climate. Short day onions do well in the shorter summer days closer to the Equator (Texas, we're talking about you) and long day onions thrive in the long summer days closer to the North Pole (e.g., Minnesota).
Our video's animated map shows the different regions for short day and long day. Intermediate day onions have characteristics more similar to the long day onions.
The day length differences between onions also signal differences in flavor and how long you can store them.
Thank you. This is the only article I’ve found that actually told me how to make my onions sweeter.