How long do temps have to be below freezing for sap to flow?

[Fun4stuff]

For example, i got down to 30 deg F for 3 hrs last night and the predicted high is 48 deg F today. Do you think sap will flow or was this not a hard enough freeze?

[Ed R]

It will run some, but not to hard or very long. My dad who was a pretty good ole time sugarmaker said that it needed to get down to 27 and that it would run good only as long as the length of freeze the night before.

[DrTimPerkins]

Depends...how warm was it before the freeze? How cold did it get and how long did it stay below freezing? Are we talking the north or south side of the tree (they can and often are very different). Air temperature isn't the important thing....wood/branch temperature is. Wood takes a good bit longer to change temperature (up or down) than air does.

This article might be helpful. https://mapleresearch.org/pub/mn2021earlyflow-pdf/

[Ed R]

Did you get any run at all yesterday? I don't see a freeze until this weekend. With all the warm temps we've had I don't know if the tapholes will be still viable. I think the syrup would be still good even where I'm at in southern mi.