The Ice Saints (IJsheiligen) are the name days of five Catholic saints in May, associated with night frost and weather change.

The Ice Saints are a group of five Catholic saints:

Saint Mamertus from Vienne (May 11): He is the patron saint of shepherds and firefighters
Saint Pancratius from Rome (May 12): The Romans brutally killed him because he would not sacrifice to the Roman gods. His name is still used for churches, schools and sports clubs.
Saint Servatius from Maastricht (May 13): Servatius is the first historically verifiable bishop of the Netherlands. Servatius of Maastricht is therefore also the patron saint of Maastricht.
Saint Boniface from Tarsus (May 14): He was killed by the Romans, during the persecutions of Christians. Since 1969, it is no longer obligatory to venerate him, but he still belongs in the ranks of the Ice Saints. His remains are in Rome in the basilica of Santi Bonifacio e Alesso.
Saint Sophia from Rome (May 15): She was killed during the persecutions of Christian. Sophie is also called cold Sophie because she is the only patron saint against night frost.Especially in Germany, her name day is used to put the plants outside, and hang flower boxes on the facade.

In some countries the number three is a holy number, sometimes Saint Mamertus is not included, and in other countries Saint Boniface is again not included. Especially in eastern Europe, people are familiar with Saint Sophia of Rome. So it just depends on where someone lives, and who is being commemorated.

The name “Ice Saints” is derived from the period in which their name days fall, from May 11 through May 15. In popular meteorology, these days are traditionally seen as the last moments in spring when night frosts can still occur. The planters take these days very serious or not serious at all, due to the climate change.

The chance of night frost after the Ice Saints is very small, but not excluded. Especially in areas with temperate climates, such as the Netherlands and Belgium, the risk of harmful frosts after mid-May is very low. It can happen, so it is still not a good thing for your vegetable garden.

The Ice Saints were an important time in the year for many people. It was a common tradition not to sow and plant in the open ground until after IJsheiligen. That way people could be sure that the young plants would not be damaged again by night frosts.

Nowadays, the significance of the Ice Saints is mostly symbolic. Most people no longer take the Ice Saints into account when gardening. Nevertheless, the Ice Saints are still known and are a nice piece of folk culture. I think I will take it serious, why not? Perhaps because of the living room and kitchen? It is kind of full with plants. What will you be doing?