Maple Sap Flow
What are the conditions/mechanisms of maple sap flow during
the Spring months? Thank you.
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
The pressure builds up when the cooled sap warms and expands the
Such weather conditions may occur in both the spring and fall.
The following should be helpful:
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
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
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Update: June 2012