The Ice Saints: Truth or Myth?

If you believe traditional farming rules and medieval lore, early summer gardening must wait until the end of Ice Saints. We take a closer look into this topic.

According to tradition, the Ice Saints bring the last cold snap of the winter, potentially leading to frost plant damage and massive crop losses. Therefore, many farmers and hobby gardeners wait until the Ice Saints pass before they start sowing plants. The Ice Saints occur between the 11th and 15th of May in our calendar. However, there are also myths that it is between the 16th and 23rd of May, which reflects the Gregorian calendar. We have considered both time slots for our investigation.

We have analysed whether this rule is true – with our?history+?data analysis tool. It visualises weather data since 1940 in hourly resolution for every point on Earth, and you can also download the data as raw data and choose between different weather models. For this specific analysis, we have chosen the?ERA5T re-analysis data?with a spatial resolution of 30km and have used the data since 1960.

For the analysis, three cities in Switzerland were investigated -?Basel,?Geneva?and?Lugano. The first chart shows the daily minimum temperatures for May from 1960 to 2022 for Basel, Switzerland. Indeed, there have been rapid drops (highlighted in blue) in temperature at the time of the Ice Saints in some years. Furthermore, the red line displays the average minimum temperature between 1960 and 2022. However, this line does not show any of the above-described temperature patterns, no analogy and no singularity that should appear during the Ice Saints' time. Consequently, the Ice Saints farmer's rule can be disproved for Basel.

The above chart shows the temperatures again in another form for Lugano and Geneva. Also, detecting any temperature pattern during Ice Saints is impossible for those locations.To conclude, May is simply the last month before summer in which negative temperatures can occur in Central Europe, even if the probability is relatively low. Thus, for the analysed locations, the minimum temperature for May fell below 0 degrees on only a few days in the previous 62 years (Geneva: 24 frost days, Basel: 3 frost days, Lugano: 0 frost days).

During the last few years, there is even an increase in temperature visible due to climate change, as the chart below demonstrates. There is a continuous increase in average temperatures for all of the 3 analysed locations. This temperature increase can be seen in our?climate change diagrams?(e.g. Lugano), which are globally available.

In summary, frost does not usually occur during the Ice Saints and is more likely to occur in exceptional cases. In general, a rise in temperatures can be observed during the last years, further reducing the probability of frost during the Ice Saints.

This week, the minimum temperatures in Europe will range between 0 and 2°C in the alpine regions and 4°C-14°C for most parts of northern and central Europe, as shown in our?minimum temperature map. The highest minimum temperatures can be found in North Italy and southern Spain, where temperatures locally rise up to 22°C. Towards the weekend, a general trend to colder weather in Europe can be observed, while temperatures below 0 refer at most to parts of higher altitudes in the Alps and Pyrenees, as our minimum temperature Map of Europe for Wednesday shows.