We have boxwoods that are exhibiting damage to the leaves in a pattern that...

Asked April 22, 2014, 9:55 AM EDT

We have boxwoods that are exhibiting damage to the leaves in a pattern that would suggest possible chemical burn. We use only calcium chloride to melt ice but we apply it with a broadcast spreader. Is it possible that the damage shown in the photo is the result of chemical burn? I thought calcium chloride was safe for use around plants (as compared to rock salt). Will the plants recover or do they need to be replaced? The plants shown face North East but we have similar damage to plants of differing orientations around the compass.

Hamilton County Ohio

3 Responses

Yes, calcium chloride has been shown to have a lower "burn potential," than regular sodium chloride or road salt. And I was prepared to say that your shrubs may have been affected more by winter burn than salt burn, until I saw the pictures that show the lower part of the plants damaged. Boxwoods are among those plants that are highly susceptible to salt damage, as you can read here: http://ohioline.osu.edu/enviro/wi98/enviro_1.html.
Michigan State University issues the following caution: Boxwood plantings along sidewalks can readily become a maintenance issue. Landscape designers should consider the salt sensitivity of plants placed next to sidewalks or other areas where salt is likely to be used. Many landscapers and lawn maintenance companies operate snow removal services during the winter. These professionals should be aware of the pitfalls associated with using deicing salts near boxwood and other salt-sensitive plants. Additionally, homeowners need to balance the need for safety by deicing the sidewalk with the potential damage salt exposure causes to adjacent plantings.
There is an abundance of information about what happens to plants with salt burn, preventing salt burn, and plants that can tolerate salt. However, there is not much that talks about remedying the problem. If you are determined to keep your boxwoods in their current location, I would recommend lightly pruning the damaged leaves. Then adopt a wait and see approach. They may leaf out again with a new flush of green leaves. They may not. If they seem salvageable, you will have to remember not to use any chemical de-icer on that sidewalk -- stick to sand or basic clay kitty litter. Or if you do replant, choose a different type of plant. You can check out salt-tolerant shrubs - rugosa roses are known for their salt tolerance and do well here.
Best of luck.

We use only calcium chloride pellets on the sidewalk and driveway. Can the damage shown be a result of this? We have fairly clear salt damage (image 1) and what I believe to be winter burn (images 2 & 3) but damage mentioned above looks different than the that shown below in that only part of the plant is affected and it is in a straight line.

As Chris noted in her response to your first question, calcium chloride just has a lower "burn potential" compared to sodium chloride (salt); it does not have a zero burn potential. Also, keep in mind that chemical injury is directly related to the rate of exposure which is why we sometimes see only a portion of a plant affected - the area that had the highest rate of chemical exposure. In fact, the image sent with the question Chris answered shows "classic" chemical injury symptoms from a deicing compound. However, we actually seldom see such "classic" symptoms with both exposure to deicing compounds as well as winter injury.

I would agree that image #1 accompanying your second question is most likely deicer damage - it would be hard to explain how some of the boxwoods escaped winter injury in such close proximity to others that didn't. However, I would not be so certain that images #2 and #3 are winter injury. While we definitely experienced winter damage to some boxwoods here in Hamilton County, we did not experience temperatures low enough to cause such complete destruction of tissue; including stem tissue. The winter injury I'm seeing and photo-documenting for teaching is primarily relegated to the outside leaves with inner leaves and stems remaining green. This includes some boxwood varieties that are we know to be sensitive to winter injury in Ohio. By the way, you are certainly not alone in suffering deicer damage to boxwoods: the amount of deicer we needed to use this winter in our area to keep sidewalks and driveways safe was unprecedented!