Spring is sprung
The grass is riz
I wonder where the Math is!

Yes, there lies a puzzle. How do plants know it is time to blossom and accept that spring has arrived? As Bill Finch said, in a recent article on the Mathematics of Spring, “You won’t find your spring on a calendar. There are millions of springs that will occur all across North America in the next few months, each unfolding in its own way, in its own time…But shouldn’t you wonder, Who told the tulip trees? Who told the red maples? Who told the bulbs that it’s spring?

Plants actually make a very sophisticated use of statistics to know when to break out in spring bloom. Their deep appreciation of the laws of probability mean that they know how and more importantly WHEN to place their bets, and thus are far more successful at taking advantage of spring than people are. If gardeners ever played poker with their plants, the plants would always win. Gardeners could learn a lot from plants about how to calculate their spring.

But what is it that plants are counting? Oddly enough, it’s usually not the warm days they plants are counting, but rather the cold nights. Most plants aren’t as gullible as people. They know better than to get overly excited by a few warm days in January. If they bloom or leaf out too early in response to a 70 degree day in the middle of winter, they could lose an entire year of reproduction or even their life to another frost.

 Instead, plants calculate the arrival of spring by keeping up with the number of hours each winter temperatures stay below about 45 degrees (degrees Fahrenheit which equals 7.2 degrees Celsius). Plants have apparently learned that this is a far more effective measure of the advance and change of the seasons.

Only when plants have a fairly precise number of cool hours under their belts do they begin to leaf out or bloom. Plants well-adapted to the northern Gulf Coast are satisfied that spring is upon us when their buds or roots or stems have recorded between 500 and 750 hours of temperatures below 45 degrees. Plants that are well-adapted to Birmingham often don’t start blooming until they’ve registered 1,000 or more hours of temperatures below 45.

Plants are much more diligent about clocking those hours than we are. And in spite of the fact that winter here is a roller coaster of warm and cold days, and that the last frost of spring is hard to predict with absolute certainty, our native plants and our heritage garden plants get it right almost every year.

But how did the plants know how many hours of cold to count down? It’s the accumulated experience of thousands of years of changing seasons that is running through their computer boards. Plants average the genetic memories of their ancestors and their own recent experience to get a pretty good idea of when they can expect the cold temperatures to recede and the warm temperatures to begin. Getting a good average greatly reduces the risk of blooming prematurely or too late.

Scientists label these mathematical calculations “chill hours.” And understanding a plant’s requirements for chill hours is a great way of determining whether that plant is suitable for growing here.”