Learn more and buy the 2015 Old Farmer's Almanac!
Reporting
Sap flows during the daytimeSap flows during the daytime when the conditions are right. You need cold nights (below freezing) and warm days (above freezing). It is the fluctuation that causes the flow of sap. During the night, the carbon dioxide cools and contracts and some sap freezes; this all creates suction in the tree which causes water from the soil to be drawn up into the roots and travel up through the sapwood. During the day, as the temperatures rise above freezing, the sap starts to flow. Then, the process repeats itself.