Frost heave stresses plants

Q. I overheard some other gardeners talking about frost heaving in their perennial beds. Is this a problem here? If so, what can I do about it?

Nikki from Boardman

A. Well, it’s not just our roads that suffer when we have a winter with freeze-thaw, then repeat, conditions. Thinking about this reminded me to check my own garden beds. I had not checked my perennials for frost heave. I came home and checked around my yard. Sure enough, there was some minor heaving going on.

What is it? Frost heave happens after the soil has been frozen and has lots of moisture. Pressure is then created from alternating freezing and thawing as the temperature swings up and down. The pressure lifts the plants up and (usually partially) out of the ground.

Cold air sinks into the ground, freezing the water, forming small ice particles, eventually forming a layer of ice. More moisture in deeper layers is drawn upward, then freezes, the ice expands, thus creating a two-way pressure, compacting the soil.

You may notice deep cracks in the soil, much like when there is a drought. The roots are exposed to cold air, are lifted, or heaved out of the soil. The roots may dry out and the plant dies, or is at least impacted negatively. It’s a vicious cycle.

What can you do? I try to keep a close watch on my perennials. I don’t worry if they are covered with snow; it provides insulation. I gently foot tap the plants into the soil, add some mulch for insulation and hope. Thankfully, I have never lost any heaved perennials. Remember, wet unprotected ground is a heave invitation. Perennials planted last fall are most likely impacted by heaving.

A good layer of mulch is the best protector. Mulch should be applied after several hard frosts in early fall. The weight of the mulch will keep the crowns and roots in the soil. The mulch also serves to keep the soil temperatures more even.

You might want to amend the soil to improve drainage if you find problems. Well-drained soils warm faster in the spring, too. Choose plants that are deep rooting. Placing shallow root plants in the ground too late in the season may lead to heaving.

Many perennials need time to develop a deep root system. This is why fall mums rarely survive the winter. If you shop at the end of season for perennials, be sure to grab some bags of mulch, too.

Here are a few perennial favorites that may suffer frost heave (shallow roots): daisies, blanket flower, coreopsis, coral bells, mums, pincushion flower and painted daisy. To be safe, plant these early in the season and all should be just fine.

Strawberries have shallow roots, so they are prone to heaving. It’s a good idea to cover your berry plants. Mulching with straw is a good choice and easier to remove in the spring.

Marilyn McKinley is an OSU Extension Master Gardener Volunteer in Mahoning County. Winter hours for the Plant and Pest Diagnostic Clinic vary. Submit questions to the clinic at 330-533-5538 or drop samples off to the OSU Extension Office in Canfield.