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Estimating the End of Maple Sugaring Season – Based on Growing Degree Days


Not so much

Today’s lack of sap flow, in the face of a 50⁰F daytime high, after a low in the mid 20’s overnight, has me concerned.  It certainly seems as if the sap should be running from the taps.  So, I thought I would revisit the issue of Growing Degree Days, and perform the calculation using data from a bit closer to home.  A couple of “revelations,” if you will: there are Celsius, or Centigrade GDD, and there are Fahrenheit GDD.  It is often not specified in literature, and I tripped over this distinction, or the lack of a distinction, in my earlier post on the subject, “MAPLE SYRUPING SEASON – STARTING, ENDING, OR BOTH?”  In the wikipedia entry on the subject of Acer saccharum, aka Sugar Maple, it is written that “flowering occurs in early spring after 30–55 growing degree days.”  GDD Celsius or GDD Fahrenheit not specified, naturally.  Since the units in the balance of the entry are in metric units, with English units noted parenthetically, I finally made the connection that flowering will occur at 30-55 GDDC (Celsius).  If GDDC is then multiplied by 1.8, the result is a GDDF (Fahrenheit) range of 54-99.  Okay, so now that that’s cleared up, where are we now?

Until now I have used South Haven data available at Wunderground to look at GDD, today I decided to get data closer to home; from our friends at the nearby OverGrown Acres Farm Wunderground weather station in Lawrence, Michigan.  After downloading the year-to-date data, I made the GDD calculation, and just out of curiosity, I also made the Heating Degree Days calculation.

Growing and Heating Degree Day calculations, from OverGrown Acres Farm weather data

Interestingly, we chalked up 9 GDDover the course of just 3 days in mid-February, so clearly the situation can change quickly.  But, at just 11 GDDF year-to-date, there seems to be no reason to think the end of the season is upon us now, with budbreak no expected to occur for at least another 43 GDDF.

So, I’ll rest a bit easier tonight, and just be thankful for the day of inside work, rest, and some much-needed time with Geri.

All the best,


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2 replies
  1. David Wildermuh
    David Wildermuh says:

    Wow. There is so much more to this than I ever knew. Thank you John. Will look forward to more information..

    • John Newell
      John Newell says:

      Of course the Indians and settlers did it with none of this newer “technology,” like 10-day forecasts, or knowledge of “growing degree days,” but like electricity I suppose, now we see these advances as indispensable. I’ll head out to check taps soon; hoping against hope, throwing up a prayer, too, that the trees flowed overnight. Thanks for reading and commenting.


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