Sugar maple foliage

Sugar maple foliage

What causes the sap to flow out of the trees?

Early in the spring, when the maple trees are still dormant, the air temperature rises above freezing during the day and drops below freezing at night. This temperature fluctuation is vital to the flow of sap. 

Here's how it work: During the periods, when temperatures rise above freezing, positive pressure develops in the tree. This pressure causes the sap to flow out of the tree through a wound (tap hole). During cooler periods, when temperatures fall below freezing, negative pressure (suction) develops, drawing water into the tree through the roots. This replenishes the sap in the tree, allowing it to flow again during the next warm period.  Although sap generally flows during the day when temperatures are warm, it has been known to flow at night if temperatures remain above freezing.

Well before colonists began sugar maple tree growing in this country, Native Americans tapped the trees for their sweet syrup and used the sugar made from it for bartering.  Their method of sap harvesting and syrup making is still used today!

Last updated March 15, 2017