With a frost warning again tonight, I thought it would be a good time to review the legend of the Three Kings.
I've written about this for the past few years, but it's one of those perennial topics in the gardening world and serves as a reminder that while it's OK in early spring to plant potatoes, peas, cabbage and other cold-tolerant vegetables, you should still hold off on tomatoes, cucumbers, squash, peppers and other tender plants.
The Three Kings, or Three Frozen Kings, is a Czech legend that serves as a warning to protect tender plants against a possible late frost. In one of various forms, the story says the three kings or saints (Pankrac on May 12, Servac on May 13 and Bonifac on May 14) were frozen when the temperature dropped while they were fishing at sea.
On May 15, St. Zofie came along with a kettle of hot water to thaw out the three frozen kings.
Since Czech immigrants found Iowa similar to their home country, those traditions carried over, and, whether or not the story makes sense, it seems sensible in many years to heed the Three Kings warning.
Knowing the last average frost date for your area can also help. That date can vary, however, depending on the source. I’ve seen that in northeast Iowa, the last average frost date is May 10. East-central Iowa is April 30, and southeast Iowa is April 20. This year, we're still experiencing frost in East-central Iowa in May - hence the "average" designation.
A U.S. Climatography report placed northern Iowa, around Decorah, with a last average frost date of May 26; central Iowa, around the Cedar Rapids area, at May 13 and southern Iowa, around Ottumwa, at May 3. Climatologists say the average can vary, even within the same county. The last frost date might be a week later in low-lying areas or a week earlier on hilltops. Because the frost date is only an average, your safest bet might be to heed the Three Kings warning and wait until May 15 to set out those tender plants.