Spring starts in the month of March. Astronomically, spring begins at the precise point in time when the center of the sun passes directly over the Equator. This moment is called the vernal equinox.
Use of the Gregorian calendar keeps the arrival of spring on March 20 or March 21 for most years, though sometimes spring arrives on March 19.
According to National Geographic, in addition to the astronomical start of spring, a biological spring begins each year, usually on a different date. Climate change researchers note that in some areas, biological signs of the arrival of spring, such as flowers blooming and snow melting, begin weeks earlier in 2014 than it did in the 1970s.