In most parts of the world, seasons are defined by a fixed date in the calendar. Thus, in the northern hemisphere 1st of September means that summer is over, and autumn has come. In the Southern hemisphere the 1st of September heralds the first day of Spring. Or does it? When is it really spring?
Most will probably say that spring in New Zealand includes the months of September, October and November. The meteorological seasons have been used for a long time, in fact since the 1780s, so any weather data recorded about the seasons from then on can be easily compared with recent data. But do you find another answer if you look in space, in nature or in the weather?
If you put on your astronomical glasses, the answer is a little different. The reason we have different seasons at all is that the Earth orbits the Sun. This means that the northern part of the globe tilts towards the Sun half of the year, while it tilts away from the Sun the other half of the year. But the "astronomical spring” does not start on September 1. It only happens about three weeks later at the so-called spring equinox. And astronomically speaking, it is the spring equinox that warns that the season is changing.
The spring equinox falls on one particular day, when the Sun stands vertically above the Equator, and the day and night are equal in length. From that day the southern hemisphere can look forward to longer days. When we go from winter to summer, the days get longer. It has an effect on animal and plant life, and that is what we experience as the change of seasons. In fact, you can say exactly when the spring equinox falls. With the astronomical definition, springtime in 2020 with start on September 23 in New Zealand.
A walk in the bush, fresh air all the way down to the lungs and a beautiful sight of spring flowers on the trees and shrubs. In New Zealand, there is another tradition of watching Mother Nature and let her changes define the season. One example is the bountiful and beautiful bloom of golden flowers on the kūmarahou (Pomaderris kumeraho). "When kūmarahou in flower, near time to plant kūmara" (Matthews 1911, Anderson 1954). When exactly this happens depends largely on how the weather behaves. Therefore, it can vary greatly when the plants assess that it has become spring. When with kūmarahou flower this year?