By Jessica Carlson 

OTC Master Gardener Intern

A common issue that often surprises homeowners is frost heaving. It can uproot or injure perennials and young shrubs over the months in our area that often have wild temperature fluctuations. Understanding why it occurs and how to prevent it can be effective in keeping your garden’s resilience through the freeze thaw cycles typical of Minnesota winters.

Frost heaving happens when soil repeatedly freezes and thaws. Moist soil expands as it freezes, pushing plant crowns or roots upward. When the soil thaws, the displaced plants may remain exposed above ground, leaving roots vulnerable to drying and freezing. Heavy clay or compacted soils, which hold moisture, are the most prone to frost heaving. The problem tends to occur during late fall or early spring, when daytime temperatures warm enough to thaw the upper layer of soil, only for it to refreeze overnight.

Perennials that form shallow root systems are especially at risk. Commonly grown examples in our region would include coral bells (Heuchera), delphinium, Shasta daisies (Leucanthemum), garden phlox, daylilies, and hostas. New plantings of black-eyed Susans (Rudbeckia), coneflowers (Echinacea), and chrysanthemums are also vulnerable until their roots are well established. Small and recently planted shrubs such as spirea, hydrangea, and dwarf potentilla can heave if not well mulched.

The best prevention is to help the soil stay consistently cold once freezing temperatures arrive. After the ground has frozen, typically in late November, apply a loose mulch layer two to four inches deep around the base of perennials and shrubs. Straw, pine needles, shredded leaves, or wood chips all work well. Avoid piling mulch directly against stems or crowns, as this can trap excess moisture and encourage rot. Of course snow is a natural mulch however we cannot always count on a consistent snow cover.

If you garden in heavy clay soil, amending beds with compost or planting in raised areas can improve water movement and reduce the freeze thaw stress that leads to heaving. Watering deeply in late fall before the ground freezes helps soil settle around roots and prevents them from drying out over winter.

By understanding frost heaving and taking preventive steps, we can protect our perennials and shrubs from winter’s toughest challenges. A little fall preparation goes a long way. For more detailed guidance, visit the University of Minnesota Extension website www.extention.umn.edu/planting-and-growing-guides/protecting-trees-and-shrubs-winter or contact your local Extension office.