Maybe you’ve heard this before: in order for the sap to flow in a maple tree and harvest it for making syrup, temperatures need to be above freezing during the day and below freezing at night. Well, we’ve been tapping maples to make syrup for several years, and I must say: assuming sap is flowing simply because it is 33°F (1°C) or above is incorrect. There are other factors at play.
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Climate Criteria for Collecting Maple Sap
In truth, temperatures need to be a bit higher than simply “above freezing”—around 45°F (7°C) seems to be more consistently the rule for us.
But wait! Even if it’s 55°F (12°C), the sap might not budge. That’s because there are other factors that allow sap to flow. Here two important factors you can also observe: sunshine and the amount of snow on the ground. Let’s very quickly break those two down.
The sun helps the sap flow
Sun shining on trees helps to increase the actual temperature the tree is experiencing. If the thermometer on the shady side of your house is reading near freezing temperatures but the tree is fully exposed to the sun, the sap could very well be flowing. And this goes both ways—on a cloudy day, even if it’s above freezing, the sap might not be flowing too well.
Snow on the ground keeps the roots cold
Not only do the branches need to warm up to pull sap through the trunk of a maple, the trunk and roots actually need to warm up too. If you have a few feet of snow on the ground, sap probably won’t burst forth on a 45°F (7°C) day. It’s obvious—snow acts as a thermal barrier that limits the impact of the sun and air on the ground. And the tree holds its sap in the ground on those cold nights. Things need to warm up more thoroughly for the sap to get going.
So even though it’s not quite as cut and dry, you can get a better idea of when the sap is flowing by taking temperature, sunshine, and snow depth into consideration.