In the Japanese calendar, the spring starts on February 4th.
The Japanese traditional calendar is lunar based, just like most eastern Asia countries. You may know that around this time of year, Chinese (and many south-eastern Asian countries) are celebrating the Chinese New Year. Well, Chinese celebrate the beginning of the spring with their new year. Japanese celebrate the beginning of the spring with Setsubun.
Soy bean and Demon's mask
Feburary 4th is right between the Winter Solstice Day and the Spring Equinox Day. In traditional calendar, this day stands the beginning of the spring. The western culture regarded the Spring Equinox Day as the beginning of the spring season, but the eastern culture regarded the Spring Equinox Day as the center of the spring season. So, the spring lasts till the day between the Spring Equinox Day and the Summer Solstice Day, which is around may 5th.
Since the Setsubun is a celebration for the arrival of spring, its tradition has survived for very long time; in fact, arrival of summer, autumn, or winter is not celebrated not as much. It's the power of spring!
Also, there are many events happens at Setsubun. Kompira ShrineSuidobashi invites Sumo wresters. If you want to see Samurai parade, check out Yoroitoshikosi at Ashikaga. Most of Shrines and temples will have some kinds of Mamemaki events. Enjoy.