Winter Review: Frost Heaving

Winter is the ideal dream time for cold-climate gardeners, but it’s also a perfect time to review good gardening practices and increase your gardening knowledge. For this Winter Review we’ll examine frost heaving.

Frost heaving can occur when winter weather brings wide temperature swings for days on end. Soil, originally frozen when cold temperatures settled in, will thaw. When the soil refreezes the ice that forms in the previously thawed layers expands. When this occurs at the base of some plants it can cause the crown and root systems to rise – or heave – from the soil, which exposes the roots to cold and drying temperatures.

If this happens multiple times, a plant can be pushed completely out of the soil. The result is a significantly stressed or dead plant.

Now factor in multiple frost/thaw cycles with heavy rainfall during an extended thaw cycle. Some of the rain settles into the top layers of soil making it even more likely to heave during a subsequent freeze.

The wide temperature swings we’ve experienced in Connecticut this winter, coupled by the lack of a constant heavy snow cover, has led to significant frost heaving. Shallow-rooted perennials – think strawberries, heuchera and scabiosa – are very susceptible to frost heaving, as are any plants in naturally moist soils and late-planted shrubs and perennials that did not have adequate after-planting time to extend their roots far into surrounding soil.

A heavy snow cover helps mitigate frost heaving. I noticed very little frost heaving after last winter, when three feet of snow blanketed my gardens and held soil temperatures constant throughout the winter. I’ve likewise found little frost heaving during winters that remain cold but have little snow cover.

If you’re a fan of frost heaving – which no right-minded gardener would be – this 2013-2014 winter weather has been ideal. We had cold temperatures and 3” to 5” snowfalls in early-mid December, but on the first day of winter outdoor temperatures were in the 50’s. By the first of January it was again cold, but all snow was long-gone until 5” fell on  January 3rd. That snow melted when heavy rains, along with a few days of temperatures in the 40’s and 50’s, followed.

January 15 brought frosty morning fog, quickly dissipated by the rising sun, and afternoon temperatures warm enough to entice this little caterpillar guy to wander.

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OLYMPUS DIGITAL CAMERANow, on January 22nd, we’re back to a deep freeze – a low of about 5 degrees this morning – and 10” of new snow.

I hope this snow blanket remains – and is replenished – until spring begins to push this fickle Old Man Winter away. Though all my plants are well mulched, which offers some protection from frost heaving, I’ve already noticed heaving of one late-planted lavender and in the strawberry bed.

Sometimes there is nothing a gardener can do to prevent frost heaving, but a good blanket of snow until spring may help protect heaved plants from further damage – it may even save them from demise.

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2 comments for “Winter Review: Frost Heaving

  1. January 25, 2014 at 5:17 pm

    I never knew what caused this before, thanks for the explanation. I’ve been rather concerned with how plants will fare this spring. Our temps are like yours, swinging wildly. We’ve had a lot of snow but there’s been a great amount of rain as well.

    • January 27, 2014 at 9:47 am

      Marguerite, I’m glad I was able to offer an explanation for you. I share your concern on how plants, particularly those planted during the autumn of 2013, are faring with the wild temperature swings this winter.

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