I shoveled Michigan sand...beach sand....around boxes during winter. I have winter...I want as much snow as I can get to fall on the trees. I don’t keep trees that won’t survive outside. The boxes and sand keep roots surviving well and no rodent camps. I have extremely cold wind chills also. I deal with the wind by putting up a green mesh fencing. It’s about 48” tall. Does the job perfectly well for the trees needing wind protection. The wind to me is more the winter problem. Once the roots are frozen in an insulated mass that keeps them perfectly fine until spring. If I know there is a potential for a frost, or just very low temperatures, in the spring I mist the trees in the evening cold to put on a good frozen layer...an ice coat. Works well.