Mamertus, Pancras, and Gervais were three early Christian saints. Because their feast days, on May 11, 12, and 13th. According to folklore 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 Poland and the Czech Republic the Ice Saints are St. Paneras, St Servatus, and St Boniface thus the dates are May 12th to the 15th There is a German legend of the ice saints has resulted in the belief that there are special “iron nights,” especially in the middle of June, which are 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.
Today I will take a look at the past weather here in Grand Rapids for not only the above dates but will expand the time frame so I will use the dates of May 11th all the way to May 18th and see if the tradition is true (or could be true).
The 30-year average high for May 11th and 12th is 68° and the average low is 46° that goes up to 69 and 47 for the 13th to the 15th and is up to 70 and 48 by the 16 to the 18th
Over the years the hottest it has been in this mid-month time frame was a hot 91° on May 15th 1991 and May 17th 1962. (during the true three chilly saint’s days of May 11th to the 13th the hottest it has been was 89 on May 11th 1922 and May 11th 1896) The coldest maximum temperature(s) a very cold on May 11th 1966 and 43 on May 11th 1981 and May 12th 1966. ( a very cold couple of days in May of 1966) coldest lows were very cold and frosty 27° on 12th 1981 and May 13th 1946 and 28° on May 11th 1907, May 12th 1946 (1946 another cold mid-May) and May 13th 1996.
I looked at the last 30 years to see if Grand Rapids has had either a frost or near frost or very cold days (with high temps in the 40’s or very low 50’s in the mid May time frame. What I found in 14 years yes and 16 years no. The years that we did have a frost, near frost (temps in the mid 30’s) or days with highs only in the 40’s or very low 50’s were 1988,1990,1994,1995,1996,1997,2001,2002,2003,2006,2009, 2010,2013, and 2014. So that means in the last 30 years there was almost a 50% chance of a frost in mid May. That should tell you it would be best to wait until after May 20th (May 17th at the earliest) to plant your Tomatoes and other frost sensitive plants.
This year May so far has been so cool that the three chilly saints have not stood out. But I would say it is now OK to plant most of your plants if you have not already done so.
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