“Some of [the results were] as expected, that certain plants just don’t tolerate any kind of salt in the soil,” says Deeter. She also noted that plants often thought of as tough—members of the Asteracae family, black-eyed Susans (Rudbeckia hirta) and purple coneflowers—were not at all amenable to salty soil.
Deeter came up with a list of highly and moderately salt-tolerant perennials, with certain grasses, hostas and daylilies being prominent. Download the complete plant list here!
Deeter’s other findings led her to conclude that just because one cultivar of a plant is salt-tolerant, it doesn’t mean the rest of its cultivars are.
She warns that seaside and salty roadside growing conditions can be different. Deeter noticed that while seaside gardens often have sandy soil that allows salt to leach out quickly, roadside gardens have heavier soils, which don’t drain well, meaning roadside beds can contain far higher concentrations of salt.
In fact, it may be far more useful to look at lists of drought-tolerant perennials when considering what to plant in beds afflicted by salt. That’s because salt mimics the effects of drought, altering soil composition so it’s harder for plants to uptake water and nutrients. “I think [salt tolerance] is closely related to drought tolerance,” says Sue Farley, gardener for the Town of Ajax, east of Toronto, “because what the salt is actually doing is creating a droughty area. It’s inhibiting plants from absorbing moisture.”
So, when Farley was researching perennials to plant in the town’s lengthy median gardens, she chose plants that could tolerate a dearth of water.
While Farley’s had a “couple of plants peter out,” she’s mostly had a lot of success. Standout performers include the ‘Hansa’ rose (Rosa ‘Hansa’), woolly thyme, perennial flax (Linum perenne ‘Sapphir’) and a range of grasses such as eulalia.
Lorne Fast, a curator, instructor and taxonomist at the Niagara Parks Botanical Garden and School of Horticulture, supervises a long border situated between the Niagara Parkway—a very busy thoroughfare that gets covered with salt—and a parking lot, which also gets salted in the winter. Though he cautions that he hasn’t done a formal evaluation as to which perennials have fared best, the border has survived for several winters now, with many plants growing well only one metre or so from the parkway. Some of Fast’s recommendations are catmint, ‘Mönch’ Michaelmas daisy and ‘Red Fox’ spike speedwell (Veronica spicata ‘Rotfuchs’).
And Carol Goodwin, professor of environmental horticulture at Nova Scotia Agricultural College, suggests trying, among others, yarrows, yellow flag iris, perennial sweet peas and lady’s mantle—which is “incredibly salt-tolerant”—in areas with salty soil.
So, although salty soil affects most gardeners across Canada in some form, there are many plants to choose from to help cope with the challenges of sodium saturation.