An excellent article explaining how salt damages plants has been published by Purdue University.  The article also includes lists of more salt tolerant plants and de-icing products recommended as alternatives to salt.   Purdue Article:  https://www.extension.purdue.edu/extmedia/id/id-412-w.pdf .  The following explanation is based on material in that article and elsewhere:

Salt is composed of sodium and chloride, both of which are toxic to plants in high concentrations.  When salt dissolves in water, the sodium and chloride ions separate, and the sodium ions in the salt replace other nutrients in the soil that plants need (potassium, calcium, and manganese), making these nutrients unavailable to plants.  Rock salt absorbs the water that would normally be available to roots, thus dehydrating the plant roots.  This changes their physiology and causes additional plant stress.  The chloride ions that are absorbed by roots are transported to leaves, where they accumulate and interfere with chlorophyll production and photosynthesis.  Further, when passing vehicles spray salt on plants, it can damage a plant’s leaves, buds, and small twigs, which in turn can reduce the plant’s cold hardiness, making tissue more susceptible to freeze damage.

Salt injury symptoms resemble drought or scorch stress.  Foliage can yellow and look stunted. Leaf margins may turn brown and curl.  Damage becomes evident through spring as new growth starts.  Evergreens react more rapidly to salt injury.  Conifer needles will turn yellow and brown.  If plants suffer leaf or needle damage only on the side of the plant facing the roadway or sidewalk, then salt damage becomes obvious.

Yews with damage from salt spray (Photo by Purdue University Extension)

What to do about salt damage?  If you have valuable plantings close to streets or other areas pelted by salt products, you can try to flush the areas with water (or, in the future, pile clean snow onto the area if that is still around).  A soil test can be conducted to indicate the actual soluble salt content, and if it presents above specified limits, gypsum can be applied to soil under the root zones of trees and other affected planted material.  This will help move the sodium through the soil.  If plantings near areas affected by salt have not survived, it would be prudent to replace them with plants that have reported salt tolerance in order to prevent a recurrence.  Deciduous planting may work better adjacent to roadways.  Some local jurisdictions that operate salt trucks are willing to reseed damaged turf grass.  (Unfortunately, this would be done in the spring, and reseeding is best done in the late summer/early fall, but it is worth a try).  Alternatively, the homeowner can re-sod the area that contains damaged turf grass. 

Be mindful that healthy plants can withstand salt injury more readily.  Therefore, it is imperative to always prepare the soil properly for planting, and to provide ample watering and nutrients (if needed) to promote plant health.

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Cover Cold Sensitive Plants

Protect Young Plants from the Cold.    Should warm weather occur later this winter, it could cause early new bud growth on such shrubs.  If so, you should monitor the weather forecasts, and if dramatic low temperatures with frost are predicted, it would be sensible to cover the most affected plants (e.g., Hydrangeas) during such nights (using row covers, or simple bed sheets).  Regardless, most shrubs thusly damaged last winter recovered nicely in the spring, particularly if simply left alone, despite their wilted appearance, until the temperatures warmed up.

In Case of Snow….  If we do have prolonged heavy snowfalls, it is important to check on any fragile shrubs and trees that could be harmed.   Newly installed plants are particularly delicate and susceptible to damage from heavy snow.  If there should be a lengthy snowstorm, periodically – e.g., every few hours – it would be wise to go outside and brush snow off of shrubs and trees (yes, even though trees look nice with snow covering their branches).  You can also shake plants to dislodge snow.  It is best to use a broom and sweep the snow lightly upwards off of the branches, starting at the top of the plant and working down. 

Remove Snow from  Evergreens.    Broadleaf evergreen shrubs are most susceptible to heavy snow damage (e.g., Nandina, Rhododendron, Mahonia, Viburnum, Pieris, Boxwood, Japanese Holly, Cherry Laurel, Azalea, Euonymus, Aucuba, etc.).  Conifers — such as Yew, Juniper, Falsecypress, Arborvitae, and Cryptomeria – are a bit hardier, but still can suffer branch breakage from the heavy snow that accumulates particularly at the top of the plant.  In fact, if tall, such plantings can be bent down to the ground by heavy snow, and it is imperative to ‘release’ them.  Otherwise, the bark can be damaged from the stress of the snow.  They may be crooked after being released, but they should straighten in the spring.  They should be viable if addressed quickly rather than letting the snow remain and damage them.   If they are young and fragile, it is worth tying them to stakes or fencing temporarily to help straighten them.  Particularly vulnerable specimens might benefit from some physical support prior to the onset of winter, particularly if heavy snowfalls are predicted.

Leave Ice Alone.  If shrub and tree branches are covered by ice, rather than light snow, then it is best to leave that until it melts, because small branches could easily be broken by efforts to dislodge the ice.

Freezing and Thawing Cycles.  Alternative freezing and thawing can also harm perennials.  This can cause plants to heave out of the ground, leaving roots exposed, causing damage or death to plants.  If it becomes very cold and snowy, plants should be inspected after temperatures moderate above freezing.  If you see any plants that appear to be lifted above the ground with roots exposed, you should try to temporarily fix this by digging up some soil and placing it around the base of affected plants to cover the roots.  Later on – late spring – it may be helpful to dig out such plants and reinstall them deeper into the ground.  A good layer of mulch should protect against this occurrence.

Snow is an Insulator.   Snow on the ground at the base of plants is actually helpful by providing insulation.  So leave it be.  Just take care not to compact the ground adjacent to your plantings by walking through the snow that is in the gardens or near the trees (except as needed to remove the snow from those plants.)

Enjoy the beauty of snow in the landscape.  But as you head out to shovel your walkway or blow the snow off of your driveway, don’t forget to sweep the white frosty covering from your precious plantings to protect them for seasons to come.

Photo credits:  (1)  Jo Ellen Meyers Sharp (Hoosier Gardener); (2) Better Homes and Gardens

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