After our recent winter, everyone with at least a shrub or two is belly-aching about winter burn on their evergreens. Count me in. 

What IS winter burn?

Wisconsin Extension’s answer as the first shown on Google (after the AI junk):

Winter burn is a common problem of evergreens including those with broad leaves (e.g., boxwood, holly, rhododendron), needles (e.g., fir, hemlock, pine, spruce, yew) and scale-like leaves (e.g., arborvitae, false cypress, juniper) grown in open, unprotected locations and exposed to severe winter conditions.  Evergreen plants that are marginally hardy in a location (i.e., not well-adapted to local winter conditions) are at increased risk for winter burn.  Winter burn can be so severe that affected plants may die and/or require replacement.

Why so MUCH winter damage? It’s not just the cold

Seeing winter burn everywhere around me, I wondered how bad WAS our recent winter, really? And to my surprise, my county’s coldest temperature during December and January was a mere 10 degree F.  That’s well within the normal range for the average low here in Zone 7B of 5 to 10 F.  (If I’m reading the map right.)

So if our winter wasn’t unusually COLD, what was it that did so much apparent damage to plants around here? Could be that our low temperatures, in the teens, lasted so damn long – weeks on end. Some plants were also harmed by the heavy load of ice on top of a heavy load of snow, neither of which melted for those long weeks in the teens. I call it the Icemaggeddon, a two-punch that also meant it wasn’t safe to take walks outdoors for weeks!  It was a shocking bummer of a winter for us spoiled mild-winter types! 

But as Wisconsin Extension goes on to explain, there are lots of contributing factors:

  • Warm fall temperatures that delay the onset of plant dormancy can also contribute to winter burn.
  • Cold injury can occur mid-winter when temperatures drop sharply at sunset causing foliage that has warmed during the day to rapidly cool and freeze. 
  • In addition, on sunny winter days, foliage (particularly foliage facing the sun) can begin to transpire (i.e., naturally lose water through the foliage). 
  • Strong winter winds can lead to additional water loss making winter burn more severe. 
  • Colder than normal winter temperatures and longer than normal winters can also be factors in the development of winter burn, especially if below normal temperatures occur into April.

 Plants that took the hit

Clockwise from upper left in the top photo:

In the top photo, upper left is a Nandina domestica that looks only slightly worse than all the ones in my neighborhood.  Its hardiness zone is 6A, so why all the leaf drop? 

At Dave’s Garden I found a list of “Plants that experience winter damage in the mid-Atlantic region, writing that ” Nandina domestica – is the most common plant to exhibit foliage damage when temperatures go below 10 degrees Fahrenheit. This variety is a semi-evergreen, meaning that it will drop leaves in a cold Winter, and stay mostly evergreen in warmer conditions. New growth begins about the same time that our native dogwoods begin to leaf after flowering around mid-April, but it can be two weeks later in a cool Spring. Within several weeks new growth opens fully and there will be little or no evidence of the problem. In most cases no pruning is needed to rejuvenate the plant since only leaves are damaged and branches and stems are not affected. ”  

The plants I’m most worried about are the 11 crossvines (Bignonia capreolata) I’m growing to provide screening.  In this case the extensive leaf burn – over half the leaves are dead – is even more curious to me because it’s hardy to zone 5.  That link adds this detail: “Above ground stems are not reliably winter hardy throughout USDA Zone 5 where they may die to the ground in severe winters (roots are usually hardy therein and will sprout new growth the following spring).”

Boxwoods seem to exhibit a lot of winter burn but it’s actually bronzing. “Boxwood bronzing is not harmful to the plant it is just lacking chlorophyll. The chlorophyll will come back once the spring warms up more so you do not need to prune this away.” Garden coach Amy Powers agrees, saying can trim away the bronzed bits or not – boxwoods will be fine either way.  These boxwoods, in a common co-op area I’ve adopted, are probably Japanese, hardy to Zone 6a.  

My Acuba’Picturata‘ always gets some burn, and I trim away those parts.  It’s hardy to zone 6b but they “do best in protected locations or warm micro-climates.  Also they’re best in part or full shade and will develop burns like this in hot afternoon sun, too.

On the left, a neighbor’s Cherry laurel (hardy to Zone 6a) shows lots of burn.  If they were mine I’d trim away the burned bits.

Dave’s  Garden cites cherry laurel in the Mid-Atlantic for  having winter damage: “Many Otto luykens and Schip laurels show damage to foliage in the first year after transplant. The cherry laurels are relatively slow to establish after planting, and may have problems with late Fall planting followed by persistent cold. After the initial Winter an established plant will rarely have problems with cold weather. In most cases a light pruning will remove dead leaves and stem tips, but more severe damage can mean a much longer period for the plant to revive, and possibly determine that the plant needs replacement.”

On the right is ‘Ice Dance’ carex (hardy to Zone 5a), which looks like this near sidewalks where it gets salt. In some spots it looks fine. 

Loropetalum victim of winter kill?

Loropetalum on the left, planted last summer, has a similar foliage color to the Ninebark on the other side of the bird bath.  Dead Loropetalum shown on the right.

For years I’d admired Loropetalum shrubs, so popular in the South, and finally decided to give one a try – to replace a Ninebark that had slowly died, which ruined the nice symmetry in the nook garden seen here. I replaced it with a ‘Ruby’ Loropetalum, which is hardy only to Zone 7a, but I hoped it would thrive in this protected spot.  Nope!

So now I’m contemplating what WILL live in that spot and screen the ugly utility wires. I’m thinking maybe an Osmanthus ‘Goshiki,’ hardy to zone 6 and evergreen.