Salt-Tolerant Plants for Drivesides and Walks in Montana

What makes a plant salt tolerant?

The term covers two separate abilities. Wisconsin Extension rates plants separately for tolerance of salt spray and tolerance of salt in the soil, and it notes the same plant can differ between them. Spray settles on buds and needles from plows, traffic and wind. Soil salt arrives with snowmelt and shoveled snow and makes it hard for roots to take up water. Both are explained in our guide to how de-icing salt damages plants and concrete.

Check both columns against your site. A bed beside a highway or a busy county road gets mostly spray from passing traffic. A bed beside your own walk, where you shovel treated snow, is mostly a soil problem. Wisconsin's list uses H for high tolerance and M for moderate, and many plants have only a spray rating. A blank in the soil column means no rating was given, not that the plant is safe.

Are there salt tolerance lists specifically for Montana?

We looked and did not find one written for home landscapes and de-icing salt. USDA NRCS's Bridger Plant Materials Center in south-central Montana did publish a technical note, MT-112 from February 2016, on 18 woody species planted across a salinity gradient in a salt-affected silty clay loam in 2006. It is a useful document for naturally saline ground. It was a non-replicated study on that site, and we were not able to read its per-species results for this article, so we are not quoting them. If your property has naturally salty soil, read that note directly.

Montana State University Extension's lists are a different help. Its MontGuide on fire-resistant plants covers species adapted to Montana, with a caution that not all of them grow in every part of the state. It points to the Tree and Shrub Selection Guide (EB123) and its perennial MontGuide (MT199903AG) for site conditions. That is the check to run on any Wisconsin plant before you buy it, and a local nursery can tell you what is reliable in your valley.

Which shrubs handle salt and are also fire resistant?

This is the shortlist we would start from, because these appear on both lists. Wisconsin rates them, and MSU's MontGuide lists them or their group as fire resistant in Montana. Shrubby cinquefoil (Potentilla, listed by Wisconsin as Dasiphora fruticosa) is rated high for spray and soil. Nanking cherry is high for both. Alpine currant is high for both, and MSU lists currants as a group. Chokecherry is moderate for both.

Mockorange, in the forms Wisconsin rates, is high for spray with no soil rating, and MSU lists Philadelphus as a group. Sand cherry (Prunus besseyi) is high for both, and MSU lists cherries as a group. American plum is rated high for spray, with MSU also listing native plum. Cotoneasters such as rockspray cotoneaster are moderate for both, and MSU lists rock cotoneaster.

Others on Wisconsin's list deserve a look even though the two lists do not overlap by name. Common snowberry, Vanhoutte spirea and American elderberry are rated high for both spray and soil. Staghorn sumac is high for both, and MSU separately lists skunkbush sumac as fire resistant, though Wisconsin did not rate that species. Check Montana availability and hardiness on each, and read the mature size so it does not overhang a walk or a plowed edge.

Which trees tolerate road salt?

Wisconsin rates thornless honeylocust, Kentucky coffeetree and Japanese tree lilac high for both spray and soil. Bur oak is moderate for both. It rates quaking aspen and eastern cottonwood high for spray, with no soil rating. Colorado blue spruce is high for spray and moderate for soil, and ponderosa pine is high for spray with no soil rating given. Remember that Wisconsin's ratings come from a different climate and we are not saying each of these will thrive on your site.

Size and location often decide it. A tree beside a driveway has to fit the space, keep its limbs above the plow and leave a place to store snow. Wisconsin also advises keeping sensitive plants at least 60 to 100 feet from highways and 30 to 40 feet from city streets, which is a useful test for a tree you already have. MSU's list includes aspen, cottonwood, ash, birch and maple among its fire-resistant trees, though it also notes that conifers as a group are more susceptible to fire damage because of their high resin content. Our tree services team can tell you what you are working with before you plant.

Which perennials and grasses work along a salted walk?

For a low strip, Wisconsin rates several perennials as moderately tolerant of spray, with some overlap with MSU's fire-resistant groundcovers and herbaceous plants: daylily, bearded iris, stonecrop (Sedum), hens and chicks, yarrow, evergreen candytuft, shasta daisy, red-hot poker and coral bells. Sea thrift is rated high for spray, and MSU lists common thrift. Note that these perennial ratings are for spray, so a bed that collects salty meltwater is still a risk.

Kinnikinnick, also called bearberry, is the standout groundcover: Wisconsin rates it high for both spray and soil, and MSU lists it as fire resistant in Montana. For ornamental grasses, Wisconsin rates Karl Foerster feather reed grass and switchgrass high, and blue fescue, blue oat grass and little bluestem moderate. One caution for fire country: Idaho Firewise's demonstration garden ranks ornamental grasses just above conifers at the least fire-resistant end of its chart, so keep them away from the closest zone around a house, and see our fire-resistant plants guide.

Should I plant juniper along the driveway?

It is the obvious plant, and in western Montana, it comes with a trade-off. Wisconsin rates common juniper, creeping juniper and savin juniper high for both spray and soil. But MSU Extension calls junipers a good example of a highly flammable plant that should not be used as a foundation plant in the urban-wildland interface, because the foliage contains volatile oils and beds around the plant accumulate old, dead material.

That is the reason we would rather see a low, deciduous salt-tolerant shrub close to a house or an attached fence, and leave junipers well away from any structure if you keep them at all. Our guide to junipers, arborvitae and other high-risk shrubs near homes sets this out, and the wider picture is in our Montana Wildfire Guide. The same caution applies to dense conifer hedges used as a screen along a drive.

Are any of these plants a problem to avoid?

Yes, check before you buy. Wisconsin's list flags several plants as restricted in Wisconsin, including Amur maple, some black locust, and Siberian peashrub, with only named cultivars or fruitless forms listed. Miscanthus is listed with a note to use sterile cultivars only. We have not checked each against Montana's noxious weed rules for this article, and it is a question to put to your nursery or your county weed district. Salt tolerance is no reason to plant something invasive.

How should you plant a salty strip so it lasts?

Placement counts as much as species. Wisconsin notes that newly planted trees and shrubs are more vulnerable because of their small root systems, so give anything new extra attention in its first winters. Keep shoveled snow off its root zone, and use burlap or snow fencing around it in late fall if it faces spray. Planting on berms keeps salty runoff away from roots, and redirecting runoff with grading or gutters also helps. Wisconsin adds that plants in sandy, well-drained soil tolerate salt better than plants in clay.

Leave a sacrificial strip where you can. A foot or two of rock at the pavement edge gives snow somewhere to go, gives the plow room, and keeps plants out of the worst of the spray. A low plant is also less likely to be damaged by snow plows or snow load. Soil testing helps too: Utah State University Extension recommends it for checking excessive salinity, and our landscaping design team can plan around the result.

Can you repair an existing strip without replanting?

Often you can buy time. Wisconsin suggests rinsing plants in winter warm spells and watering deeply in early spring to flush salt below the root zone, at least 6 inches of water, and it suggests gypsum on heavy clay soil high in salt. Maryland Extension suggests 1-inch soakings three to four times in spring. If an edge fails year after year, the honest answer is often to reduce the salt: use sand for traction, keep melting products for the steps, and move the snow pile.

Can HJ plant and clear the same property?

Yes. We do landscaping as well as snow and ice work, so we can design a drive edge with winter in mind, and agree in the fall where snow and product go on that same edge. We cannot promise any plant will survive a salted strip, and we will tell you when a location is the problem. This article is part of our Montana Winter Property Guide. Call (406) 215-7319 or ask for a free estimate and we will walk the property with you.

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