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Understanding cold weather foliage discoloration

HAVE YOU EVER NOTICED wintertime discoloration on some of your shrubs, only to see that they look fine as the weather warms up in spring? Some plants can develop what we call winter bronzing. A few commonly affected plants are arborvitae, holly, juniper, azalea and, perhaps most notoriously, boxwood. 

This color change occurs in response to winter temperatures, and it is uniformly distributed on the foliage. Because evergreens will still photosynthesize in winter, they need to replace the water lost to photosynthesis, which can be difficult when the soil is frozen. Winter bronzing is often more enhanced on certain species, following a fall drought and when there are lots of warm sunny days where the soil is still frozen. While winter bronzing is a stress response, it is not the same as winter injury or foliage disease. 

We are seeing signs of winter injury on many plants, especially on broadleaf evergreens, from the arctic blast we experienced in December. The severity of the damage will vary depending on the type of plant, as well as its location, health and age. 

To help prevent this type of stress in your landscape, water evergreen shrubs well before freezing temperatures arrive. Maintain a mulch layer of 2 inches or so to retain moisture and insulate the root system. If a wintertime discoloration is winter bronzing, it is temporary and will no longer be noticeable as warm weather returns and new growth begins. 

While it may be hard to look at now, don’t panic and start cutting things down or removing them just yet. Always wait until spring to fully assess any wintertime color change with your evergreens. If you are concerned that you may have winter damage on your evergreens instead of winter bronzing, consult your local horticulturist, plant expert or trusted garden center for care assistance and to help determine the best course of action.

SHELLY NOLD is a horticulturist and owner of The Plant Kingdom. Send stories and ideas to her at The Plant Kingdom, 4101 Westport Road, Louisville, KY 40207 

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