Planting in a Berm
Location: N. Carolina mountains, near Boone See many putting in berms this summer for shrubs and perennials due to rocky soils. We get much freezing and thawing. My concern is, won't the plants' roots freeze (even with mulch, which doesn't stay put well on a slope)?
Certified GKH Gardening Expert
Berm construction can take on many forms, making it easy to "craft" the type that works best for your area. Mulch, like shredded bark, is most recommended for sloping areas. Evergreen ground covers can also be implemented and will help hold mulch in place while creating a nice insulating cover for dormant plants. If the proper plants are chosen for your particular region and its growing conditions, there should be little worry of the roots/plants freezing. The following articles should be of some help
to you: https://www.gardeningknowhow.com/special/spaces/creating-and-using-berms-in-the-landscape.htm