Question:
What is frost heaving, and how do I prevent it?Answer:
What is Frost Heaving?
Frost heaving occurs when repeated freezing and thawing of the soil surface during winter pushes shallow-rooted perennials upward, exposing their crowns and roots. As water in the soil freezes, it expands and lifts the plant; when the soil thaws and settles, the plant often does not return to its original position. This can leave roots and crowns exposed to cold temperatures, drying winds, and injury.
Plants with small or shallow root systems are prone to heaving. This includes newly planted perennials that have not had enough time to fully establish and root in before winter arrives.
Species that are prone to frost heaving include coral bells (Heuchera), strawberries (Fragaria), mums (Chrysanthemum), pig squeak (Bergenia), pincushion flower (Scabiosa), seathrift (Armeria), foamflower (Tiarella), shasta daisy (Leucanthemum), and hen-and-chicks (Sempervirens), among others.
How Do I Prevent Frost Heaving?
To help prevent frost heaving, leave healthy plant debris in place over winter to provide some insulation. For plants that are particularly susceptible, apply a 3 to 4-inch layer of mulch over the crown after the ground has frozen, usually by late November in Iowa. Applying mulch too early can delay dormancy and increase the risk of winter injury. In early spring, once the soil begins to thaw, gradually remove the excess mulch, typically around mid-March, to allow new growth to emerge.
The mulch helps prevent the soil surface from heating up and cooling down during sunny winter days or periods of warm temperatures mid-winter. This helps the root zone of the plant to maintain a consistent soil temperature, preventing the freeze-thaw cycles that work roots and crowns out of the ground. Avoiding late-season cultivation that disturbs roots and late-season planting can further reduce the risk of frost heaving.