I'm currently building a 10X100 fungal/garden bed, in a USDA zone 4A environment, and am going to want to keep the soil warm enough to keep fungi spreading. How deep will I want a layer of wood chips to try to keep the area warm enough, but not so warm that it it's like a sauna into the spring. I can tell you that the creek running about 10-20 feet away only develops a thin layer of ice in the dead of winter due to the natural bacterial environment of bog bacteria.
Lots! What's wrong with a sauna? Fungi love a good sauna! I would have around 3 ft of inoculated woodchips/cardboard layered with hey: