May is a strange weather month in Northern Europe. The past few Aprils in Frankfurt have had a high number of quite warm and sunny days, even if they start out with cool temperatures in the mornings. As May began, however, the temperatures have headed south, or, gone down. You have the heat running, and the wind and rain have had an extra cold bite whenever you leave the house. This has a long tradition in Europe, and it has a name. The “Eisheiligen” refers to a period in May when, according to popular farmers’ lore, the weather is still too unstable to plant crops because of the danger of frost.
The Ice Saints (Eisheilige in German, les Saints de Glace in France) is a name given to St. Mamertus, St. Pancras, and St. Servatius in Flemish, French, Dutch, Hungarian, German, Austrian, Polish, Swiss and Croatian folklore. They are so named because their feast days fall on the days of May 11, May 12, and May 13 respectively. In Poland and the Czech Republic, the Ice Saints are St. Pancras, St. Servatus and St. Boniface of Tarsus (i.e., May 12 to May 14). To the Poles, the trio are known collectively as zimni ogrodnicy (cold gardeners), and are followed by zimna Zośka (cold Sophias) on the feast day of St. Sophia which falls on May 15. In Czech, the three saints are collectively referred to as “ledoví muži” (ice-men or icy men), and Sophia is known as “Žofie, ledová žena” (Sophia, the ice-woman). The period from May 12 to May 15 was noted to bring a brief spell of colder weather in many years, including the last nightly frosts of the spring, in the Northern Hemisphere under the Julian calendar. The introduction of the Gregorian calendar in 1582 involved skipping 10 days in the calendar, so that the equivalent days from the climatic point of view became May 22–25.
In Sweden, the German legend of the ice saints has resulted in the belief that there are special “iron nights,” especially in the middle of June, which is susceptible to frost. The term “iron nights” (järnnätter) has probably arisen through a mistranslation of German sources, where the term “Eismänner” (ice men) was read as “Eisenmänner” (iron men) and their nights then termed “iron nights,” which then became shifted from May to June.
People used to believe that it was not safe to plant crops until after the Ice Men were gone. There’s also a proverb in England: “Ne’er cast a clout till May be out.” A “clout” being clothes, as in “Don’t take off your winter clothes till the end of May”. It’s kind of reassuring that those ancient weather observations still apply, what with climate change and all that.
Scientists have been unable to determine that there really is a higher chance of frost in May, but anytime the weather dips from warm to cool in May, Germans start talking about the Ice Saints.