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Name: John
Location: N/A
Country: N/A
Date: N/A

What are the conditions/mechanisms of maple sap flow during the Spring months? Thank you.

Hello John,

I know a little about this topic even though I am from Illinois which is far from the heart of maple syrup country.

Sap flows from a maple tree by internal pressure caused by the expansion of the sap which changes in density with changes in temperature and atmospheric pressure. There also needs to be free (unfrozen) water available for roots to absorb).

Generally, when you have a good temperature contrast between night and day the sap will flow. Cold nights down in the 20s (fahrenheit) followed by day time temps in the 50s with sunny conditions are ideal.

Sap reaches its maximum density at about 38 degrees. So as the tree cools the sap inside contracts allowing more sap to be absorbed through the roots. Of course, if the ground is frozen, this can't happen. If the ground is thawed and water is available through snow melt or rain then a conditioning process occurs allowing pressure to build up in the tree.

The pressure builds up when the cooled sap warms and expands the following day.

Such weather conditions may occur in both the spring and fall.

Wayne Vanderploeg

Dear John,

The following should be helpful:,5716,120804+3,00.html


Anthony R. Brach, Ph.D.

The mechanisms are complicated and not all that well understood. For a basic introduction to maple syrup production, see this site (my personal web site for River Trail Nature Center etc.):

There is a link there to Quebec maple syrup producers that has additional information. I have a book at my office, which I don't have at hand here, that has a lot more detail; if you want that reference email me directly and I will look it up.

J. Elliott

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