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SALT TOLERANT PERENNIALS
With winter in the north comes salt applied to roads and walks to melt snow and ice. Such salt can damage the roots of nearby perennial plants. There are several herbaceous perennials fairly tolerant of winter road salt.
If you’ve ever tried to get salt out of a salt shaker during humid weather, you’ve seen the affinity of salt for water and moisture. The same principle applies in soils, with the salt pulling moisture away from the roots. This results in root “desiccation” or drying out.
Another way perennials can be injured is from the sodium and chloride ions, which make up salt, separating. Chloride ions are readily absorbed by the roots, transported to the leaves, and accumulate there to toxic levels. It is these toxic levels that cause the characteristic marginal leaf scorch seen during the growing season.
If salts build up in pots, growers can flush them out by heavy watering. This is not so easily done in soils. Instead, if on your own property, use “plant safe” products such as those deicing materials derived from magnesium or calcium chloride, or a mix of these with kitty litter (not the sawdust kind which doesn’t provide traction).
Another option, and perhaps the only one along roads, is to plant perennials tolerant of high salt levels. At least with perennials, that die back to the ground each winter, you don’t need to be concerned with salt spray to foliage as you do with woody plants and evergreens.
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Some of the hardy (generally USDA zone 5 or colder) perennials listed as highly salt tolerant include some columbine and pinks (Dianthus), bearberry, common wood aster, daylily species and hybrids, bird’s foot trefoil, seaside goldenrod (Solidago sempervirens), and barren strawberry (Waldsteinia). The latter is a great low groundcover for dry shade, quite underutilized. Its yellow flowers in early summer resemble those of strawberry plants. ‘Karl Foerster’ reed grass, blue lyme grass, maiden grass (Miscanthus), muhly grass, sand cordgrass, and little bluestem are ornamental grasses reported salt tolerant.
Hardy perennials with at least some salt tolerance include silver mound artemisia, butterfly weed, candytuft, foxglove, sea holly, peony, baby’s breath, tall phlox, creeping phlox, bellflower, Lenten rose, coralbells, bearded iris, evening primrose, ‘Autumn Joy’ sedum, hens and chicks, Russian sage, Prairie mallow, soapweed, sea thrift (Armeria), yarrow, and yucca. ‘Elijah’ blue fescue is a low ornamental grass with some salt tolerance, as is ribbon grass (Phalaris), panic grass (Panicum), blue oat grass, and fountain grass (Pennisetum). Keep in mind the latter can be quite root invasive so needs proper placement. Don’t plant ribbon grass where it will crowd out other desirable plants, or where root pieces can wash with rains through streams and ditches to colonize elsewhere. The least tolerant hardy perennials for salt include purple coneflower, hosta, narcissus, and thyme.