The Aftermath of the Polar Vortex

Written by: Tony Arnoldi, Board Certified Master Arborist WI-0102B

Posted: 2019 | Plant Health Care | Summer | Tree and Shrub Care

It has been nearly 30 years since a polar vortex of this magnitude hit our area. Back then, that cold snap had actual temperatures of minus 28 and minus 30 degrees over 2 consecutive days that were critical. The polar vortex from this winter reached minus 26 degrees for at least 2 days. Both events did considerable damage to susceptible trees, shrubs and perennials.

This damage resulted from the cold temperatures that were lower than the plant tissue could tolerate, and bud, branch and trunk tissue were severely injured or killed. Exposure mattered and some plants were killed by sustained winds that touched them, while plants of the same species or cultivar in a different exposure in the same yard escaped significant damage.

Trees and shrubs that are less than fully hardy for this hardiness zone were the most susceptible. Examples are Japanese Maple, Paperbark Maple, Golden Rain Tree, some cultivars of Redbud, European Beech, some Hybrid Elms, Limber Pine, Concolor Fir, Burning Bush, Privet, Burkwood Viburnum, Doublefile Viburnum, Rose of Sharon, Beautybush, Junipers, Boxwoods, some Hydrangeas and Roses, among others.

Also noteworthy was the observation that the polar vortex added damage to trees that had various pre-existing conditions such as borer damage, or fungal infections like tip blight. These trees may even be cold-hardy otherwise, but extra damage from cold injury happened on struggling or weakened plant parts.

The first response should be to allow up to a full growing-season to pass before deciding if the plant must be removed or pruned to attempt to save it. In some cases, those portions that were under snow cover during the critical lowest-temperature intervals were spared. In other cases, terminal buds were killed but given time, dormant buds were able to awaken and show where life still persisted along branches that might otherwise have been cut off. Still, by now most cases have become clear as to what was able to survive. Some buds may have initially started to grow, but then collapsed under the strain of hot summer days because the ability to move water out to the extremities of the branches was too curtailed by underlying cold damage.

For trees and shrubs that sustained this damage, it is important to provide cultural care that helps the plant in its recovery. Watering (and monitoring for too wet or too dry soil) is extremely important. Enhancing root system function through root bio-stimulants, compost teas, and incorporation of beneficial mycorrhizae can compensate as well. Pruning is important to improve appearance, health, safety, and to clear the way for re-growth.

Trees and shrubs are valuable! Be sure you are taking the appropriate actions by consulting with your local Wachtel Certified Arborist. He or she can help you make wise decisions in dealing with the aftermath of this terrible cold snap.