Frequent temperature cycles above and below freezing cause water near the soil surface to freeze, expand, and pull up more water from underground. This causes desiccation underground and, due to pressure, compaction. The ice layers near the ground surface create pressure that displaces soil, rocks, hardscape material and plants (perennials, trees and shrubs). This can expose plant roots to cold air and cause their desiccation, which can sometimes lead to the death of the plants.
What to do:
Frost heave usually starts in natural dips in soil. Keep an eye on those locations and rake them out and add compost wherever you see cracks where roots could be exposed. If the ground allows, you can try tamping dislodged plants back into place. You can also add a layer of mulch, like pine needles or straw, on top of the soil after frost has occurred to insulate it from further freeze-thaw cycles.
When planting a new plant, make sure to plant it correctly by ensuring that the soil level of the garden matches the soil level of the pot that the plant came in.
Author: Veronica Lanz, MG, Vancouver Chapter