At 8" down in the soil and according to Washington State U, the ag sites never had any of their locations at below 30°f this winter ..!
Lots of snow made lots of insulation. At 4', we figure it's 55° year around and 32° water from the melting snow took the frost right out of the ground. Doesn't always work that way, here. Too often, we have lots of sub-freezing weather with little or no snow cover.