Boxwoods are broadleaf evergreens that store their energy in their leaves over the winter. They don’t tolerate winter wind and extreme cold temperatures. This past winter caused a lot of boxwoods to show symptoms of winter injury and/or desiccation.
Desiccation occurs when the ground is frozen and the broadleaf evergreen leaves lose moisture faster than they can take it in. When the ground is frozen, they can’t absorb water easily, thus the leaves end up looking “burned.” This is called winter burn.
Death of the steams occur with temperature extremes and can also be connected to potentially dry soil. Regular readers know that I preach this, “Don’t let plants go into the winter dry.”
Our soil was dry in December, leaving plants a bit stressed. They get a double whammy – cold temperatures along with dry roots. My colleagues and I suspect that this led to some of the damage we are experiencing this spring.
According to the Ohio Agricultural Research and Development Center weather data in South Charleston, OH, we were almost three inches below normal for precipitation in December. Thus, most plants were likely dry when they got hit with the extreme cold temperatures.
Boxwoods have leafed out in our area by now. You should see new growth on stems. If you don’t, those stems are likely dead. Pruning is necessary to clean out the dead and allow new growth to begin filling in.
Some who have contacted me have been told that they boxwoods have boxwood blight. When they send me photos, it is clearly not boxwood blight, but winter injury.
Or it could also be boxwood leafminer that I wrote about a few weeks ago. The symptoms for this pest show up on last year’s leaves with the new growth hiding some of the damage.
Be sure to get a proper diagnosis before acting, particularly if you are going to use pesticides.
Most of our plants have leafed out by now. If you still have some that haven’t, look at the stems to see if there is any green tissue under the bark. Be patient and they may leaf out or may not.
If you are out of patience, cut out the dead or what looks dead and new growth will eventually fill in.
In the case of the boxwoods, since they are broadleaf evergreens, it will take them longer to fill in than deciduous plants. I know some people who contacted me will likely replace the entire plant.
I am also seeing some plants with damaged leaves. They leafed out only to be hit by freezing temperatures this spring. They will eventually leaf out again.
Pamela Corle-Bennett is the state master gardener volunteer coordinator and horticulture educator for Ohio State University Extension. Contact her by email at bennett.27@osu.edu.
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