Tapping for Syrup

What: Charlotte and Nathaniel are tapping Boxelder trees for syrup. Encountering this friendly and industrious pair on my walk home from work, I stop to converse with them about their project.
Where: In the Near North neighborhoods of Minneapolis, near Bassett Creek
When: Wednesday, March 13, about 5:30 pm
Observer: Abbie
Conditions: How do you know when the sap is rising? Charlotte tells me the thermometer gives the signal. When nights are still 32 or below but days warm up above freezing, that's when a maple's stored sugars are traveling up from the roots and out to the branches.