Frost Heave
Frost Heave is likely the cause of plant failure more than we even know
Frost heave is a common problem leading to the demise of plants in the North and Midwest, and we often don’t even realize it happened. What exactly is frost heave? As air temperatures drop below freezing, moisture in the soil begins to freeze. As the water freezes it expands, swelling the soil and moving plants. As soil temperature continue to drop more and more moisture freezes and can eventually expand enough to push plants up out of the ground.
Once the plants start to move from the swelling soil, roots are broken which can cause some damage to the plant. Cycles of freezing and thawing can actually make the situation worse be creating layers of ice. As more moisture is created in a thaw and then freezes in another layer it continues to create barriers for downward movement. Our plants, or anything else, will move in the path of least resistant, which has now become up because of the ice barriers. If plants heave up out of the soil the roots are fully exposed to extreme temperatures and drying winds. Many plants will not survive the situation at all.
There are a few things we can do to prevent frost heave. Probably the most important is to be sure we have well drained soil. The plant experts and gardeners preach that all the time for so many reasons, but well drained soil will definitely help to reduce frost heave. Be sure you work plenty of organic material into your planting beds.
Additionally you can avoid planting too late into autumn. You want to be sure your plant is plenty of time to establish strong anchoring roots. So if you plant late be sure you allow at least 6 weeks before frost. You should also apply a deep layer of mulch around plants. Mulch acts as an insulator, not to keep your plant warm but to help maintain more constant soil temperature. Wait for at least a couple of hard frosts to apply mulch and your soil and any moisture will freeze very slowly and then maintain the cold with its’ blanket of mulch to help prevent thawing.
If you have planted in fall or have new susceptible plants be sure to keep an eye on them over winter. Watch for plants that appear to have a “mound” of mulch rather than level with the rest of the garden bed. The crown has likely heaved up. It is best to remove the mulch and add soil around the crown, then replace the mulch. Trying to press the plant back into the soil will either not work at all or compress and damage roots. You may want to replant deeper next spring.
Speaking of susceptible plants, yes some are more susceptible to frost heave than others. Even if you have chosen good hardy plants appropriate to your zone, that does not guard them from heaving problems. Shallow rooted perennials are the most susceptible, and some may need several years to establish a strong anchoring root system.
Be sure to plant the following perennials early in the season to establish roots and avoid frost heave:
Blanket Flower, Gaillardia
Coral Bells, Heuchera
Coreopsis
Foamflower, Tiarella
Foamy Bells, Heucherella
Lilyturf, Liriope
Mums, Chrysantemum
Painted Daisy, Tanacetum
Pigsqueak, Bergenia
Pincushion Flower, Scabiosa
Seathrift, Armeria
Shasta Daisy, Leucanthemum
Whirling Butterflies, Gaura
Most shrubs and trees are a bit sturdier than perennials, but do keep on eye on seedlings with minimal root structure. And of course keep an eye on low areas of the gardens and any areas where drainage is a problem. Then take care of those issues next spring!