Why Plants Need Winter Insulation

I like gardening words and phrases because they’re often quaint. One of my favorites is asking someone if their perennials heaved. No, it doesn’t mean the plants were sick to their stomachs. It means the perennials literally heave up out of the ground when their roots are torn from the freezing and thawing action of the soil during winter and spring.

How do we stop our perennials from heaving? They need insulation. If the soil lies bare all winter, the ground can thaw and refreeze as temperatures fluctuate. One of the best insulators is Mother Nature’s snow cover, which does a great job of moderating soil temps. Unfortunately it’s not always there when we need it. Or it doesn’t last.

That’s why we cover perennial beds and strawberry patches with mulch in late fall or early winter. One or two feet of mulch helps greatly. It’s best if it’s applied after the ground is frozen, because most northern perennials need a winter cold treatment.

Insulating mulch or snow cover keeps cold temperatures from penetrating so deeply into the soil, and also keeps the ground consistently frozen. This stability prevents destructive freezing/thawing cycles.

The most available and useful mulches for insulation are leaves and straw. Even several inches are helpful, if more isn’t possible. The mulches can even be added over a little snow, if snow comes early, and mulches are still available.

For perennial beds that weren’t mulched in the fall, winter protection can still be given. While shoveling snow during winter, toss extra onto perennials and strawberries. The increased depth will help the snow last longer if we get mid-winter thaws.

Leaves or straw should be removed in spring after severe cold is past, but before new growth begins on trees, shrubs, and flowers.

If your own plants have been safely nestled under a blanket of insulation, next spring you can ask someone else, “So, did your perennials heave?” It usually brings a fun, quizzical look. Until next time, “Happy Gardening!”