The first day of spring in Ireland falls on February 1, according to the Celtic calendar.

An excerpt from the article 39 facts about Ireland

It is related to the Celtic festival of Imbolc. This holiday was supposed to mean cleansing by "fire and water", and was dedicated to the Irish goddess of spring, poetry, healing, and crafts, Brigid. The earliest mentions of Imbolc in Irish literature date back to the 10th century.

Currently, this holiday is celebrated as Saint Bridget's Day.