Note: The original draft of this post was written on April 7, 2018.
Walking around a neighborhood in the Maryland suburbs of D.C. earlier this year, evidence of winter burn appeared on street after street: hollies, azaleas, euonymus, rhododendron, even nandina, crisp-edged, the outermost leaves appearing blow-torched, dead. What happened?
Insufficient water the previous year, freezing nights regularly followed by much warmer days, and drying winter winds combined to create this disturbing effect. Broadleaf evergreens – hollies, azaleas, euonymus, nandina – are particularly susceptible. Unlike deciduous plants, broadleaf evergreens retain their leaves all year. If the days as well as nights remain cold, the plants go dormant, suspending photosynthesis, the mechanism by which they feed themselves and fuel their growth. But when freezing nights repeatedly alternate with daytime temperatures in the 40s, 50s, or higher, the plants may take advantage of the warmth and sun and begin to photosynthesize.
Photosynthesis requires water, which plants pull out of the ground by their roots, up and out through their leaves in a process called transpiration. If plants are established and sufficiently irrigated in the months before winter, they may have stored enough water to support winter transpiration. But if the stored water is insufficient, and the plant’s roots cannot absorb water from the frozen ground, the leaves become dehydrated – water continues to flow out through the leaves and evaporate without being replaced. Add to this scenario the wild wind of this past winter, and leaves begin to die.
The result is a plant that appears fatally damaged, an unattractive focal point in the landscape. But pay closer attention, and you should see that while the leaves are brittle and brown, the plant’s branches are living. Scratch a half inch or so of a branch with a knife to be sure: if you see brown, there’s a good chance the branch is dead, but most likely you will see green, indicating living tissue.
What is the treatment for winter burn?
First, do not prune. This may be difficult if you’re bothered by a plant that appears to be dying, but if you prune, you’ll probably remove the emerging foliage the plant needs to recover. As new foliage grows, dead leaves will drop or be hidden.
Second, water damaged plants as soon as you can and continue watering as needed, through spring and summer but also fall and winter, not stopping until the ground is frozen.
Third, check the references under ‘More on Winter Burn’ and you’ll find suggestions for treatment, recommendations for prevention, and additional explanations of what causes winter burn.
The photos below show a Nellie Stevens holly progressing from winter burn to new growth.
More on Winter Burn
Botts, Beth. “How to help damaged evergreen shrubs rebound from ‘winter burn’.” Chicago Tribune, March 16, 2015. http://www.chicagotribune.com/lifestyles/home/ct-sun-0322-garden-morton-20150316-story.html.
“Desiccation or Winter Burn.” Missouri Botanical Garden. Accessed May 13, 2018.
Higgins, Adrian. “Winter-battered plants may look dead — but don’t give up on them yet.” The Washington Post, March 28, 2018. https://www.washingtonpost.com/lifestyle/home/winter-battered-plants-may-look-dead–but-dont-give-up-on-them-yet/2018/03/27/e5ad4e2a-27d8-11e8-bc72-077aa4dab9ef_story.html.
“Winter Damage – Trees and Shrubs.” University of Maryland Extension, Home & Garden Information Center. Accessed May 13, 2018. https://extension.umd.edu/hgic/winter-damage-landscape-plants.
“Winterburn.” Chicago Botanic Garden. Accessed May 13, 2018. https://www.chicagobotanic.org/plantinfo/winterburn.