I kind of don't get this. Even under 4" - 6" medium/light mulch, the plants are going to get down to what ever ambient temp is unless there is a heat source to push back the cold to the other side of the insulation.
Have my containers of plants right up against each other and they are buried in a mixture of leaves, dried grass clippings, pine needles and the like. Have the plants buried in the same stuff right up to the top most foliage. The tallest plant leaves are literally flat against the mulch layer. They kind of look like lilly pads floating in a brown/tan pond. So, there is maybe 6" of medium/light density mulch over the crowns. There is maybe a foot of mulch around the outside of the containers and mounded up the tops of the leaves.
My assumption here was to leave at least some of the foliage exposed to the sunlight so photosynthesis can carry on at what ever level it can in what ever the ambient temp.
Is this enough protection?
How does this layer of mulch actually protect the crowns and next years buds. The temp is going to stabilize though the entire mass and down into the soil?
Should I be keeping a compost pile good and active and bury the containers in that to provide some warmth?
Are tunnel covers the way to go?