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Why are the leaves on my boxwood brown?

Winter damage on boxwood.
Photo: Mary H. Meyer, UMN Extension
You can see the damage in many Minnesota landscapes--broadleaf evergreens like boxwood, rhododendrons, vinca and pachysandra covered with brown leaves, particularly on the tops of these plants. So what happened?

Damage report

The 2018-19 winter took a toll on these plants. When it was cold in December and January, before snow covered these plants, their leaves were frozen and killed. This was not so much normal desiccation or drying out, as it was outright death by extreme low temperatures when the plants had snow cover.  The damage is just showing up now. Record snow came later after leaves were exposed and open to killing temperatures.

I planted this boxwood knot (see above image) on the north side of my home in 2004, 15 years ago. This year it shows the most winter injury ever, because normally it is covered with snow and protected from extreme temperatures.

Hardy broadleaf evergreens

Due to our rigorous winters, only a few broadleaf evergreens will survive in Minnesota. Boxwood, rhododendrons, vinca and pachysandra are four common broadleaf evergreens for USDA Zone 4.

Tips for plant rejuvenation

What can we do now? For my boxwood, I am waiting to see how it regrows. If the branches are alive, new buds will grow and cover the brown leaves.  Pruning off the brown leaves too soon will leave misshapen plants.

Stay tuned for how my boxwood will look in mid summer. I usually prune it once a year in late June after new growth has come. This year with the late spring, no sign of new growth so far.  So my pruning may be later this year, but I always do it by July 15 to allow for any new growth to harden off before yet another winter.

Can I prune it now?

If you are inpatient and not too concerned about the overall shape of your brown evergreens, you can start to prune your plants at the tips by removing brown foliage.  Look for green stems and signs of life. Some evergreens you might be able to shear off the brown needles or leaves, without sacrificing the overall shape or appearance of the plants.

After mid summer and some pruning, we will all decide if the plants look too strange in shape and need to be replaced, or if we can live with the shape as they grow back to normal.

Can I prevent this from happening again?

Photo: Mary H. Meyer, UMN Extension
Protecting evergreens with burlap or blocking the wind is a good idea to prevent desiccation or drying out. Watering in the fall prior to winter is important if there is not consistent rain. Mother Nature, we hope, will send the snow to cover these broadleaf plants and help them through the extreme temperatures.

It is not realistic for me to cover my boxwood knot. Hopefully the snow will come normally and prevent this from happening in the future.

For more information see this Extension article on how to protect your trees and shrubs in the winter.

Author: Mary H. Meyer, Extension Horticulturist and Professor
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