"I’m curious to know what has caused the leaves on some of my boxwoods to turn orange during the past two months."
Here’s a snippet of our answer:
“If exposed to full sun and frequent frost and wind, the foliage of some boxwood may become orange or bronze in the winter …”
This is really quite common especially in certain boxwood varieties such as the small-leaved Korean Boxwood (Buxus microphylla var. koreana).
In fact, the other morning when I was taking pictures in the Viette gardens, I noticed that the Korean boxwood in front of an outbuilding had a very definite orange/bronze tint while the boxwood right beside it, a different species but growing under the same conditions, was still a nice healthy green color. The contrast was striking and a neat display of the seasonal variation that can exist between two different species.
Even more interesting is the fact that only one side of the Korean boxwood is showing the bronzing of the leaves; namely the side that faces west and is exposed to the prevailing winds and the sun. The side that faces the building (which is about 8 feet from the hedge) is still green except for some bronzing near the top where branch tips are more exposed. This provides pretty good evidence that the bronzing occurring here on this particular variety is due to the environmental effects of sun and wind. The building is definitely providing the boxwood with protection from the elements.
There are certain things you can do to help protect boxwood and other evergreens from sunburn and winter winds that might cause discoloration of the foliage.
Most important is to keep them watered during the winter especially when the ground is not frozen. Gardeners often forget that evergreens continue to function physiologically (albeit at a reduced rate) throughout the winter. Cold winter winds can suck moisture from the leaves and if this water is not replaced through uptake by the roots, winter injury can occur. This is why it is important to water your evergreens deeply in the late fall before the ground freezes. During dry winter weather when the ground is not frozen, be sure to check your evergreen trees and shrubs and water deeply if necessary. This is especially important during a mild winter like we’ve been experiencing so far this year. The addition of a layer of mulch will help retain the soil moisture.
Feed your boxwood in the spring and again in the fall with a slow release organic fertilizer like Espoma Holly-tone or Plant-tone to keep them healthy and vigorous.
Spraying evergreens with an anti-desiccant like Bonide Wilt Stop will also help to protect them from winter injury by forming a soft, clear flexible film over the leaves. In colder areas, the more tender broadleaf evergreens like Camellias and some varieties of boxwood and hollies should be sprayed with Wilt Stop and then carefully wrapped in burlap for additional protection from sun and wind.
The answer, continued:
“The good news is, though many consider it unattractive, this bronzing will not kill the boxwood and they should green up again once temperatures warm up in the spring.”
Personally, I think this winter “off-color” adds some interest to the boxwood – sort of like “fall color” in the winter! And keep in mind that for some boxwood like the Korean boxwood, this color change is normal during the winter months.
It is important to note that the overall bronzing of the foliage that I am talking about here is a seasonal discoloration, not winter kill. Winter kill is permanent and must be pruned out in the spring – but that’s another story …