The snowy season has finally come upon us here in Southern Ontario and along with the snow comes snow plows and salt trucks. Why is salt so damaging? What can you do to protect your sensitive plant material from salt damage? What can be done to treat plants that have been damaged by salt?
Why is salt so damaging?
Rock salt or Sodium Chloride (Na Cl) is commonly used to deice roads and walkways. As a de-icer it is fast, easy to use, effective and affordable. On the down side though, its corrosive nature is damaging to vehicles, roads and pathways. This same salt can also be very damaging to plant material.
There are 3 ways in which salt can damage your plant material.
1. Damage the soil: As the salts accumulate in the soil the soils structure can actually begin to change. These changes increase compaction and reduce aeration, and water infiltration. Soil pH also increases as salinity increases and beneficial soil microbes, especially Mycorrhizal fungi, can be harmed…these fungi help plants to take up nutrients.
2. Salt spray can burn the tissues of plants and cause them to de-hydrate: On city roadways plants up to 30’-40’ away are at risk.
3. Excess salt in the soil can cause plants to de-hydrate: Salt is a highly absorbable compound which binds very tightly with water. As it binds with the water that water becomes unavailable to the plants and even though there may be plenty of moisture in the soil the plants may experience de-hydration. Salt even has the ability to draw water from the roots, thus de-hydrating them. If the condition persists the plant will eventually die.
What can you do to protect your sensitive plant material from salt damage?
▪ If you are able to avoid the use of salt then this is your best bet. For times when this is not possible, like in the case of cities salting roadways then your best defence is to plant materials that are less sensitive to road salt…like Day Lilies (Hemerocallis), English ivy (Hedera helix), Liriope sp. , Russian sage (Perovskia atriplicifolia) Feather Reed Grass (Calamagrostis acutifloria), Switchgrass (Panicum virgatum), Bluestem (Andropogon), Sea Thrift (Armeria maritima), Fountain Grass (Pennisetum alopecuroides), Green Ash (Fraxinus Americana), Junipers
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▪ Stay away from sensitive plants like: Box wood (Boxus), Daffodils, Eastern Redbud (Cercis Canadensis), Red Osier Dogwood (Cornus sericea), European Filbert (Corylus avellana), Sugar Maple (Acer saccharum), Eastern Pin Oak (Quercus palustris), Silver Maple (Acer saccharinum) and Serviceberry (Amelanchier spp.).
▪ Construct a physical barrier around sensitive plants: This barrier may be made of plastic, burlap, or snow fencing. Whatever it is made of install it several inches from the plant you are trying to protect, placing the barrier between the pavement (the source of salt) and the plants.
What can be done to treat plants that have been damaged by salt?
▪ Flush out the root zone of effected plants to at least a depth of 6”. (If the soil is badly compacted you may need to first aerate the soil in order to assist the water in infiltrating).
▪ Apply Gypsum to the affected area. In heavy clay soils (the ones most likely to accumulate high levels of salt) the gypsum will displace sodium ions with calcium ions. This will help to improve both aeration and drainage and allow the salts to be leached from the root zone.
'Winter Salt Injury and Salt Tolerant Landscape Plants' by Laura G. Jull, associate professor of horticulture and Life Sciences, University of Wisconsin-Madison and University of Wisconsin- Extension Cooperative Extension.