Protecting Plants from Deicing Salt
Rock salt harms plants two ways: spray that dries out buds and needles, and salt that builds up in soil until roots cannot take up water. Shovel first, le...
Published by ThriveThyme
winter salt damage deicing trees and shrubs road salt
The Short Answer
Deicing salt damages plants in two separate ways. Spray thrown up by traffic dries out buds, twigs, and evergreen needles. Salt that washes into the soil pulls water away from roots and builds up year after year (University of Wisconsin-Madison Extension, UMass Extension).
You can cut most of that damage without giving up safe walks:
- Shovel and plow first, then treat only what is left (Wisconsin).
- Use sand or another abrasive for traction where you do not need melting.
- Keep salty snow off beds and lawns when you shovel.
- Flush beds with at least 6 inches of water in early spring. That leaches out about half the salt (Penn State).
- Plant salt-tolerant species within 30 to 60 feet of pavement.
Salt tolerance is not the same as immunity. UMass Extension puts it plainly: salt tolerant does not mean injury free.
What Deicers Do to Plants
Sodium chloride, or rock salt, is the cheapest and most widely used deicer, and it is also the most damaging (Wisconsin, UMass). Salt leaves the pavement two ways: it dissolves in meltwater and soaks into the soil beside the walk, or it gets thrown into the air as spray by traffic and wind.
Spray. Wisconsin reports spray moving hundreds and even thousands of feet from salted roads. Penn State gives up to 1,000 feet. Most spray damage lands within 60 feet of the road, but sensitive plants show symptoms much farther out (Wisconsin). The spray pulls moisture out of buds, young shoots, and evergreen needles, so the tissue dries and dies.
Soil. Salt binds tightly with water. Even in wet soil, a high salt level creates an artificial drought, and at high enough concentrations it draws water back out of the roots (Wisconsin, Penn State). Sodium also elbows aside calcium, magnesium, and potassium, so plants take up salt instead of the nutrients they need. Chloride moves into the leaves and interferes with photosynthesis.
The damage looks like this:
| Plant type | What you see | When it shows |
|---|---|---|
| Deciduous trees and shrubs | Leaf edges browning, off-color foliage, stunted leaves, fewer and smaller flowers, twig dieback, tufts of shoots below dead tips, early fall color and leaf drop | Early spring, or months after the salt went down |
| Evergreens | Needle tips turn brown or yellow and the discoloration moves down the needle, twigs die back, damage worst on the side facing the road | Late winter to early spring |
| Lawns and perennials | Dead patches along walks and drives, especially where runoff collects | Spring greenup |
| Soil | Crusting, poor drainage, poor aeration, compaction | Builds over several years |
Soil salt injury is slow. Wisconsin notes it develops over several years rather than in one season. UMass says symptoms can appear in summer, or even years later, which is why salt is easy to blame on something else.
One timing detail matters. Salt applied in late winter and early spring does the most damage, because plants are waking up and moving water again (Wisconsin, UMass). Early winter applications give rain a better chance to leach the salt away before roots get active.
Newly planted trees and shrubs are the most vulnerable. They have small root systems and little stored water (Wisconsin).
Prevention
1. Shovel before you salt
Wisconsin's advice is to remove snow and ice with a shovel, snow blower, or plow first, then apply deicer to what is left. A light application before a storm keeps ice from bonding to the pavement, which makes the next shoveling pass easier and uses far less salt.
2. Use the least damaging product you can
| Product | Melts down to | Cost compared with rock salt | Notes for plants |
|---|---|---|---|
| Sodium chloride (rock salt) | About 20 F | Baseline | Most damaging. Corrosive to concrete and metal. |
| Calcium chloride | About -20 F | About 10 times | Still injures plants. Works at lower temperatures. |
| Potassium chloride | About 0 F | About 10 times | Still injures plants. Also sold as a fertilizer, which does not make it safe on beds. |
| Calcium magnesium acetate (CMA) | About 20 F | About 40 times | Does not harm plants and will not damage soil structure. Poor at melting existing ice. |
| Sand, crushed rock, ash, kitty litter | Does not melt | Low | No plant injury. Provides traction only. |
Sources: University of Wisconsin-Madison Extension, Penn State Extension.
The cheapest safe move is a blend. Wisconsin suggests mixing less than 5 percent salt with an abrasive. Their example: 1 pound of deicing salt mixed into 50 pounds of sand makes a workable traction mix for a walkway. Penn State and UMass both recommend calcium chloride, potassium chloride, or magnesium chloride over rock salt when used as directed, since none of them contain sodium.
Do not use bagged fertilizer as a deicer. Wisconsin warns that fertilizers burn roots.
3. Keep salty snow off the garden
- Shovel away from beds, not into them. Plowing or throwing salt-laden snow onto a border concentrates the salt exactly where roots are (Wisconsin, UMass).
- Aim the snowblower, not the shovel, at the lawn edge if you have to pile snow somewhere.
- Direct runoff away from planting beds with a gutter, a shallow swale, or a grade change. Wisconsin notes this works on well-drained soil and much less well on clay.
- In areas where soil salt is already a problem, plant on a low berm. A raised, mounded bed keeps salty runoff from settling into the root zone (Wisconsin).
4. Build a barrier for evergreens
A screen of burlap, plastic sheeting, or snow fencing set up in late fall blocks spray on the road side (Wisconsin, UMass). Set the screen a few inches away from the foliage rather than wrapping the plant, so air still moves. Keep the screen off the ground so snow does not pile against it.
Anti-transpirant sprays and dormant oils do not prevent salt spray injury (Wisconsin).
5. Choose the right plant for the spot
This is the only permanent fix. Wisconsin recommends keeping salt-sensitive plants at least 60 to 100 feet from highways and 30 to 40 feet from city streets.
Arborvitae is a common hedge along roadsides and a poor choice there. Penn State calls it very salt sensitive. Eastern red-cedar tolerates both spray and soil salt, and deer leave it alone.
Spring Cleanup and Flushing
Salt does not disappear when the snow melts. It sits in the top foot of soil until water moves it down and out.
Flush the beds. Penn State reports that 6 inches of water leaches out about 50 percent of the salt. Wisconsin gives the same 6 inch figure. Do this in early spring, before growth starts, and again after a heavy rain if you still see leaf edge burn. Flushing works on well-drained soil. On heavy clay it does much less, because the water runs off instead of moving through (Wisconsin, UMass).
Take a soil test if you suspect a buildup. Wisconsin notes that a soil salt test confirms the diagnosis, and that samples should be taken in early spring before rain leaches the salt out. Leaf and stem tissue can also be tested for chloride during the growing season.
Add gypsum on clay. Penn State recommends gypsum at 40 pounds per 1,000 square feet to displace sodium, and notes it will not change soil pH. Wisconsin agrees gypsum helps on heavy clay that is high in salt. Adding organic matter and improving drainage helps too.
Rinse the plants. On a mild day in late winter, before buds break, hose off the foliage and twigs to wash away salt deposits (Wisconsin). This does not fix soil salt, but it removes what is sitting on the plant.
Wait before you decide a plant is dead. Deciduous damage often does not show until growth starts, and a shrub that looks bare in April can push new shoots in May. Prune out dead wood once you can tell live from dead.
Fix the source. Replace a damaged plant with a tolerant species, or move the plant back from the pavement. Otherwise you will repeat this every spring.
Salt-Tolerant Plants
Wisconsin rates each plant separately for spray tolerance and soil salt tolerance, because the two are not the same. Their ratings are High (H), Medium (M), or blank where they had no rating. The last column lists other extension sources that also name the plant.
| Common name | Type | Spray | Soil | Also listed by |
|---|---|---|---|---|
| Eastern red-cedar | Evergreen tree | High | High | Penn State, UMass |
| Common juniper | Evergreen shrub | High | High | UMass |
| Creeping juniper | Groundcover | High | High | |
| Colorado blue spruce | Evergreen tree | High | Medium | Penn State, UMass |
| Mugo pine | Evergreen shrub | High | Penn State, UMass | |
| Austrian pine | Evergreen tree | High | ||
| Scots pine | Evergreen tree | High | ||
| Thornless honeylocust | Shade tree | High | High | UMass |
| Kentucky coffeetree | Shade tree | High | High | |
| Ginkgo | Shade tree | Medium | Medium | |
| Common horsechestnut | Shade tree | High | Medium | UMass |
| Hedge maple | Shade tree | High | UMass | |
| Northern catalpa | Shade tree | Medium | Medium | |
| Cockspur hawthorn | Ornamental tree | High | Medium | |
| Bur oak | Shade tree | Medium | Medium | |
| Northern red oak | Shade tree | Medium | Medium | UMass |
| Japanese tree lilac | Ornamental tree | High | High | |
| Staghorn sumac | Large shrub | High | High | Penn State, UMass |
| Gro-Low fragrant sumac | Low shrub | High | High | |
| American elderberry | Shrub | High | High | |
| Common snowberry | Shrub | High | High | |
| Northern bayberry | Shrub | High | High | |
| Arrowwood viburnum | Shrub | High | ||
| Bearberry | Groundcover | High | High | |
| Karl Foerster feather reed grass | Ornamental grass | High | ||
| Switch grass | Ornamental grass | High | ||
| Daylily | Perennial | Medium | Penn State | |
| Hosta | Perennial | Medium | Penn State |
Sources: University of Wisconsin-Madison Extension table of salt-tolerant landscape plants, Penn State Extension, UMass Extension.
Plants to keep away from pavement, per UMass and Wisconsin: red maple, sugar maple, littleleaf linden, eastern white pine, Norway spruce, eastern hemlock, Douglas fir, pin oak, boxwood, red twig dogwood, black walnut, serviceberry, and most viburnums.
A word about conflicting lists. UMass puts serviceberry among the sensitive plants. Penn State recommends it as a salt-tolerant shrub. Both are working from field observation, and tolerance varies within a species and with soil type. If a plant shows up on both lists, treat it as a maybe and give it some distance from the road.
Next Steps
- Check your deicer bag this week and note what is in it. If it is straight sodium chloride, plan to switch or blend.
- Set a shoveling rule for the household: snow goes on the lawn side, never into a bed.
- Order a burlap or snow fence screen for any evergreen within 30 feet of a salted walk.
- Mark a spring reminder to flush beds with 6 inches of water before growth starts.
- Pick two or three tolerant replacements for anything that burned last winter, and note the spacing from the pavement.
- Mulch new trees and shrubs before the ground freezes, which also buffers salt damage and winter drying. The Winter Mulch Desk gives depth and timing by plant type.
- Water dry soil deeply going into winter, since drought stressed plants handle salt worse. The Fall and Winter Tree Watering Desk works out gallons from trunk size.
Sources
- University of Wisconsin-Madison Division of Extension, Winter Salt Injury and Salt-tolerant Landscape Plants: https://hort.extension.wisc.edu/articles/winter-salt-injury-and-salt-tolerant-landscape-plants/
- Penn State Extension, Minimize Deicer Damage with Salt Tolerant Plants: https://extension.psu.edu/minimize-deicer-damage-with-salt-tolerant-plants
- UMass Extension, The Impact of Salts on Plants and How to Reduce Plant Injury from Winter Salt Applications: https://www.umass.edu/agriculture-food-environment/landscape/fact-sheets/impact-of-salts-on-plants-how-to-reduce-plant-injury-from-winter-salt-applications