On St. Patrick’s Day it is customary to wear shamrocks and/or green clothing or accessories (the “wearing of the green”). St Patrick is said to have used the shamrock, a three-leaved plant, to explain the Holy Trinity to the pagan Irish. This story first appears in writing in 1726, though it may be older. In pagan Ireland, three was a significant number and the Irish had many triple deities, a fact that aided St Patrick in his evangelisation efforts.The wearing of the ‘St Patrick’s Day Cross’, especially in the World War I era, by the Irish, was also a popular custom. These St Patrick’s Day Crosses have a Celtic Christian cross made of paper that is “covered with silk or ribbon of different colours, and a bunch or rosette of green silk in the centre.”
The colour green has been associated with Ireland since at least the 1640s, when the green harp flag was used by the Irish Catholic Confederation. Green ribbons and shamrocks have been worn on St Patrick’s Day since at least the 1680s.Green was adopted as the colour of the Friendly Brothers of St Patrick,an Irish fraternity founded in about 1750. However, when the Order of St. Patrick—an Anglo-Irish chivalric order—was founded in 1783 it adopted blue as its colour. This led to blue being associated with St Patrick. In the 1790s, green became associated with Irish nationalism when it was used by the United Irishmen. This was a republican organisation—led mostly by Protestants but with many Catholic members—who launched a rebellion in 1798 against British rule. The phrase “wearing of the green” comes from a song of the same name, which laments United Irishmen supporters being persecuted for wearing green. Throughout the 19th and 20th centuries, the colour green and its association with Saint Patrick’s Day grew.