Deicers: Safety Versus Salt Damage
Written by Susan Donaldson
Tuesday, 01 January 2008
I can always tell when winter has arrived. In place of layers of dead bugs accumulating on my car windshield, I accumulate a smear of salt. Salt was first used in the 1930s, prior to the advent of the snowplow, on snowy roads to make them safe and drivable. Now, in addition to plowing, during storms and when roads get icy, state, county, and city roads crews use a mixture of sand and salt to melt ice and maintain traction and safety on roadways. Sand is used to help provide traction, while salt is used to decrease the temperature at which water will freeze, keeping it liquid at lower temperatures. Washoe County uses about 490 cubic yards of a 3-to-1 mixture of sand to rock salt annually to treat 535 miles of road. Homeowners and business people also often use rock salt (sodium chloride, or table salt) on slippery sidewalks and driveways.
While salt is a necessary part of winter road and walkway safety, it does have its drawbacks (beyond my dirty windshield). We tend to focus most of our attention on the damage salt does to cars. Its corrosive nature contributes to rusting. Salts can also damage concrete, including bridge infrastructure. And, when the ice and snow melt, all that salt has to go somewhere. Unfortunately for your plants, it often winds up on landscaping.
Salts injure plants in several ways. The chloride ion is considered the most toxic element of deicing salts, causing much of the direct plant tissue damage. When salt sprays from puddles onto plants as cars drive by, it may scorch leaves or kill buds and twig tips on deciduous plants, especially during spring. Pines in general are especially noted for their sensitivity to roadside deicing salts. When affected, pine needles may become pale green, yellow, or brown in late winter. If dying vegetation is on the side of the plants facing the road or driveway, the damage has likely been caused by salt spray.
Accumulation of salt in the soil also makes it difficult for plant roots to absorb water. Excess sodium affects soil structure, and may result in poor infiltration and increased erosion. The sodium ions can displace essential plant nutrients, decreasing soil fertility. Salt accumulation in soil will also inhibit seed germination of grasses and wildflowers.
The level of damage varies, depending on the concentration of salts in the water running onto your plants, the amount of snowfall, the timing of rains that may help wash off the foliage, the type of soil, and the condition of the plants. Healthy, mature plants that are not drought-stressed will withstand salts better than newly established, young plants.
There are several deicers on the market, each having different properties (see table below). For the best selection, purchase products early in the season. If you wait until the big storm hits, you may not have many choices. Be sure to read and follow product instructions carefully.
In addition to selecting less toxic deicers, follow these tips to minimize salt damage to plants.
- Don’t use deicing salts adjacent to sensitive plants.
- Shovel early and often. Scrape away as much snow and ice as possible to minimize the need to use salt.
- If you must use salt, mix it with sand to reduce the amount needed. You only need about a handful of rock salt per square yard treated.
- Don’t shovel salt-laden snow and ice onto plants.
- Construct temporary barriers using plastic, burlap, or snow fencing to keep snow piles off plants.
- Wrap newly planted conifers with burlap to protect them from salt spray.
- Plant salt-tolerant species in areas where salt use cannot be avoided (see table below).
- If plants have been exposed to excess salts, wash off the foliage, and irrigate thawed soils to help move the salts out of the root zone.
- Water plants every three weeks during winter if precipitation has not fallen, to help avoid plant stress.
Beyond causing plant damage, recent research about the effect of deicers has focused on water quality concerns. Because salty road runoff flows, untreated, via storm drains into local creeks and rivers, it adds to the amount of total dissolved solids and sediment in our local waterways, making it difficult to meet regulatory limits. Road maintenance departments help reduce salt runoff by storing their salt mixtures in the eye-catching mushroom-like domes found along freeways. They also install sediment canisters on drainage structures to trap sand and salt and keep them out of our rivers.
What can you do to keep salt out of our waterways? Whenever possible, use less salt. Remove snow before it becomes compacted, and let the sun melt the residue. When traction is needed, use sand alone or consider using an alternative deicer, such as calcium magnesium acetate. Substances such as ash and kitty litter should be avoided, as they do not melt ice, and instead tend to glom together in a sticky mess that gets tracked into your house. With a little careful planning, your plants will stay healthy, and river water quality will benefit.
For more information on salts, deicers, and water quality issues, contact Susan Donaldson, University of Nevada Cooperative Extension, 784-4848 or firstname.lastname@example.org.
Susan Donaldson is the water quality and weed specialist for the western area of University of Nevada Cooperative Extension.
|Calcium magnesium acetate||
|Sodium chloride (rock salt)||
|Urea (46% soluble nitrogen)||
|Trees||American elm||Black locust|
|Pin oak||Quaking aspen|
|Red maple||Red oak|
|Sugar maple||White oak|
|Evergreens||Douglas fir||Austrian pine|
|Hemlock||Colorado blue spruce|
|Red pine||Jack pine|
|White pine||Mugho pine|