Maple Syruping Season – Starting, Ending, or Both?

I have been asked that question a lot lately, sometimes in more general terms, and I have asked it of myself as frequently!  Unfortunately I have had nothing resembling an answer.  Then yesterday, my early homesteader education continued, as the concept of “Growing degree days,” Gdd or GDD for short, came to my attention.  As it turns out, there is some science that can be brought to bear on the subject of when trees will bud out, and that so-called “budbreak” signals the end of the maple sugaring season.

According to the USDA Forest Service (, “Sugar maple trees seldom flower until they are at least 22 years old; flowering is heavier at later ages. The flower buds usually begin to swell at or slightly before the leaf buds show activity and reach full bloom 1 to 2 weeks before leaves emerge. Flowers appear between late March and mid-May, depending on the geographic location.”

And according to the Wikibooks entry for Acer sacharrum (, “flowering occurs in early spring after 30-55 growing degree days.”  Perfect.  What is a growing degree day?  Is “budbreak” the same as “flowering?”  When we talk about “budbreak,” are we talking about flower buds, or leaf buds?  To answer the last question first, flower buds, which as noted break well before leaf buds.  The USDA ( defines budbreak as “The start of growth from a bud.” That’s all perfectly clear, even if the buds are 50-60 feet off the ground, but of course, by the time budbreak can be seen, the need for forecasting it has been overcome by events.

So, back to the definition of Gdd.  Wikipedia has us covered here (

Basically, find the average temperature for the day; the high temp minus the low temp, divide by 2, add the result to the low temp.  Voila, that is the average.  For every 1ºC that this is above 10ºC (the “base” temperature for growing degree days), count that as 1 “growing degree day.”  Or, in Fahrenheit terms, for every 1.8ºF the average is above 50ºF (again, the base temperature), count it as 1 Gdd.

Below is the temperature history for January through February 16 in South Haven, MI.

No “growing degree days” in January in South Haven, MI

We came awfully close to a Gdd in January, with the max Mean Temperature at 50ºF, but did not quite make it.

No “growing degree days” through February 16 in South Haven, MI

The good news is that we have not even taken the first step in our march towards the 30 Gdd “necessary” for Sugar Maples to break bud.  Now South Haven is about 16 miles to our northwest, but on Lake Michigan and the Black River, so it is possible that it is warmer there than here.  Against that possibility, I also checked the history in Kalamazoo, about 30 miles to our east; no Gdd there either so far this year.  There are other factors not taken into account in this analysis, including moisture levels and cloud cover, but, at least we have something to work with.

The tip off to this (to me) new information, was the Ohio Maple Blog, a product of The Ohio State University Extension.  Thank you to Les Ober:

I hope you are having a great day.  Kind regards,


#PrimalWoods #PrimalWoodsSugarers #PrimalWoodsLife

Like and Follow us on Facebook at
Check us out on Yelp!
nd have a look at our YouTube channel at

0 replies

Leave a Reply

Want to join the discussion?
Feel free to contribute!

Leave a Reply

Your email address will not be published. Required fields are marked *