Ask A Master Gardener – Wild Wisconsin Weather

We have been on a wild ride this year with the winter weather: snow, ice, polar vortex, high winds, and more snow. How has this effected the landscape plants and invasive insects?  There is good and not so good news.

First, let’s consider the insects. The significant cold we experienced did effect some insects like the emerald ash borer and my personal not-so-favorite, Japanese beetles.  The emerald ash borer may show up to a 75% mortality rate, according to P.J. Liesch, a UW-Madison entomologist.  However, their reproductive capacity is so great that in a couple of years the population will recover.  A single female can lay upwards of one hundred eggs, making a come-back quite likely.

The frost level will be a determining factor in Japanese beetle survival. According to Liesch, during the cold spell of 2013–2014, the population was knocked back for several years.  However, these insects have a natural anti-freeze in their bodies and the snow cover we had during the polar vortex provided some insulation which may have trumped the cold. Again, the females have a great reproductive capacity with will enable them to rebound in a relatively short period of time.

Next, let’s take a look at the precipitation. Snow is a mixed blessing.  It has great insulating value and will protect tender roots from the excessive cold we experienced.  However, too much snow on plants like arborvitae can damage the limbs or simply cause them to hyperextend to the point that they do not recover.

Ice is a whole different ball game. Ice can coat the branches of many plants causing them to break completely.  Trying to break off the layers of ice will cause damage to the overwintering buds, so avoid this practice.

What about the excessive cold temperatures? If you were one of those persons who was flirting with danger and planted something that was marginal in our zone 5a, this was the year you lost.  Plants hardy to zone 5a can tolerate temperatures down to -15 to -20°, but we did get some early morning temperatures below that mark.  Branches, trunks, and, more importantly roots may have all been damaged.  Physical damage to the plants will be obvious once spring arrives.  Some trees and bushes may simply not leaf out and are dead.  If a specimen was marginal going in to the winter, it likely will not make it.  The more tender plants, such as magnolia, redbud, and peach trees will be the hardest hit.  There is nothing that can be done at this point, but watch and wait.

Lastly, the wind can be a factor in winter plant damage. Because evergreen trees and bushes continue to lose water all winter long, they are the most effected by the wind.  They suffer from dehydration when high winds buffet them and they are in a situation where they cannot take up more water, like when the ground is frozen.  This phenomenon, referred to as “winter burn”, commonly shows up when spring hits and we see brown patches and dieback on the plant.

As Brian Hudelson, a UW-Madison plant pathologist says, “All of the winter death and destruction provides ample opportunities to plant new and exciting trees and shrubs (and even herbaceous plants), and watch these new plants grow and mature.”

Carol Shirk

Certified Master Gardener

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