No sap coming from holes after drilling

[Marj]

This is my first year tapping and have a question about sap flow. I have a large black walnut grove on my property and decided to try tapping some of the trees this year. I tapped ten trees a couple days ago and when I drilled the holes on eight of them the sap began flowing immediately, however the holes on two of the trees were completely dry after drilling. I tried drilling an additional hole in both trees but those were dry as well. When I collected sap yesterday I looked at the holes I had drilled on both trees and they were still dry... no sap dripping at all. Both trees are 14" in diameter. I believe all of the trees had leaves last year so am not sure why there is no sap. Any thoughts would be greatly appreciated!

[DrTimPerkins]

Were the two dry holes on the north side of the trees perhaps? Those will take a bit longer to thaw...still fairly early in the season, especially for walnut.

[Marj]

All of the trees were drilled on the south side. I checked the holes again today but they are still dry so will keep an eye on them. Hopefully the sap will begin flowing once it warms up a bit more. I collected 3 gallons of sap today from the other eight trees (yesterday I got 2 1/2 gallons). Thanks very much for your reply!