The lone voice of horticultural reason

“Moisture in the soil increases frost depth in winter”

Exactly wrong. The more moisture in the soil as winter and freezing temperatures arrive, the less frost depth through winter.

Even in northern regions, soil temperatures are a constant fifty-degrees or so five or six feet deep. This heat rises, and the more moisture content in the soil above, the more this moisture conducts the heat. By watering your shrubs and plants well in the fall, up to the point when the topsoil begins to freeze, frost is minimized, not exacerbated.

Don Engebretson
The Renegade Gardener