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Plants, snow and deicing agents

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As I write we are getting flurries and the forecast calls for some frigid temperatures (by now we are experiencing them). We have called to have our old furnace serviced to hedge our bets against frozen pipes as the heat pump struggles to keep up with single digit temperatures. The firewood is staked and ready to stoke the Buckstove for overnight; and if the sidewalks get slick we have a stash of deicing agents. As the winter season unfolds consider the effect that deicing agents have on your plants.
Snow has an insulating effect, which is particularly useful when we do have frigid temperatures. Ground level snow will actually protect the roots and crowns of perennial and woody plants but you may notice a little burn above the snow level when it comes to broadleaf evergreens. Snow offsets excessive transpiration (moisture loss through foliage) when it comes to broadleaf evergreens like holly, rhododendron, boxwood, magnolias and mahonia. We often see “winter burn” caused by desiccation on such plants if we have a cold blistery winter. A snow cover helps to prevent it.  
Most plants grown in Kentuckiana can withstand below freezing temperatures; it is the desiccation caused by deicing agents that may be the real culprit for damage if not used properly. If you use certain deicing agents you may encounter some ragged looking plants once the spring thaw begins. Common deicing agents come in several forms: sodium chloride (rock salt) is probably the hardest on plants; calcium chloride and potassium chloride, if used excessively, can leach into the soil at dangerous levels for plants but they will not cause the same foliar burn as rock salt. However, calcium and potassium chloride are preferable over rock salt by far.
It used to be that plant lovers used fertilizer products such as ammonium nitrate and ammonium sulfate as deicing agents but these can be very hard on your cement surfaces so surely there is a middle ground for all to be safe. Basically try to avoid using products that have sodium in them, which harms plants; and avoid ammonium-based products if you are worried about your cement. Instead try fireplace ash or cheap kitty litter; they won’t melt the snow but they can provide reasonable traction on walkways without causing injury to plants.
We do not have control beyond our own landscapes and while the salt brine used to keep our roads clear is fabulous do understand that it may cause desiccation and injury along our roadways and in parking lots. While the brine is a vast improvement over rock salt spread everywhere it may still spray or leach into soils once the big thaw begins. Salt spray damage is usually replaced by new foliage come spring but salt leached into the soil can have more injurious effects.
Salt-contaminated soils can damage plant roots, which means it cannot take up nutrients and moisture; contaminated soils can also make some minerals unavailable for absorption by plants (resulting in yellowing foliage due to chlorosis). The stress of it all can make trees more susceptible to things like cankers, rot and wilt diseases which would otherwise not affect a healthy tree. The more snowfall we have the better when it comes to salt contamination because the snowmelt will help wash much of the salt through the soil, beyond the root system. Early spring rains can do the rest.  
Some plants are more tolerant of salt including many oak species and ornamental pears. Those that are intolerant include other favorites such as birch, sugar maple and beech so if you suspect salt stress for these species you may want to flush the salt from the area by watering once the ground thaws.