When I first decided to write a book on bloom times and told my landscaper friends about it, I got a surprising amount of resistance from some of them.

“But bloom times can vary so much from year to year!” they would say. “How can you be so sure of the dates?”

I doubted myself at times, but as my observations began to pile up year after year, I saw the amazing regularity with which events in the natural world occurred. I realized where the skepticism was coming from.

It’s human nature.

Just like this winter will long be remembered as one of the coldest and snowiest in recent memory for many people, it is human nature to dwell on atypical seasons and give them more weight than the many more numerous “normal” seasons that pass by more quietly.

We remember the year that the witchhazels bloomed in January, but ignore the ten years that they did not. We remember the year that spring was delayed for a month, but pay little attention to the years when things ran according to schedule. How often have you heard someone say, “How about this average weather we’re having!”? We don’t realize that most years, the weather is usually in the range of “normal” and that most plants bloom on time.

I recently came across a list of peak bloom dates for Yoshino cherries in Washington, D.C. dating back to 1921. I was curious to see how confident I really could be in predicting bloom dates by the calendar.

The respected Wyman’s Gardening Encyclopedia discusses this same list in the entry on “Order of Bloom.” In typical sensationalist fashion, the authors are quick to point out the wacky years–that one year out of dozens when the Yoshinos bloomed on March 20 and the four years that they didn’t bloom until April 15.