Protect Your Landscape Plants from Salt Damage

There are a variety of areas around the home that we wish to keep free of snow and ice. You probably don't think of all of these, but I name several because we also use these same areas for planting favorite shrubs, borders, perennials, ornamental grasses etc.. These include patios, sitting areas, decks, outdoor fireplaces, pet shelter pathways, garbage can enclosures, play equipment areas, garage and driveway, and most commonly walkways whether they're paving stones, gravel, steps, or sidewalks. Of course, the main concern is safety for anyone traveling these routes.

Even if you've done all the homework about plant hardiness, disease and insect resistance, growth rate and size at maturity, planting site and maintenance requirements, there is a single element that you may have overlooked: deicing salt resistance or tolerance. It is now time, before we are submerged in frigid temperatures and rapid ice buildup, to take a closer look at our home grounds planning and plantings. Which areas are likely to receive lots of sunshine? Less salt needed? Which are likely to stay in shade? More salt needed? Which areas are least well drained or likely to receive excess runoff or ice buildup. What to do here?

If any of the above mentioned areas are intended to be kept open during the winter, and, I'm sure several are for convenience, consider not using a lot of rock salt if you have valued plantings nearby. They might have been put in as accents, borders, focal points, screens, enhancements at the end of the driveway, what have you. The message is that salt buildup in soils can inflict serious and sometimes fatal damage to favorite plants, trees and shrubs. The younger are most at risk.

Here is how it works. Spreading rock salt or a variety of other ice melting substitutes on surfaces you wish to keep free of ice results in what might be likened to a drought for the plant material. As the soil temperature approaches the low 40s F, the finer roots of trees and shrubs begin to wake up and seek water for the first growth spurt of the year. In nature usually the water in the roots has a higher concentration of minerals than the surrounding ground water and the water will flow to the root cells to equalize the mineral concentration and supply and nourish the demand. When the mineral concentrations of the ground water is higher from accumulations of dissolved salts, root growth is impeded. Excess sodium and chloride interfere with the normal uptake of water as well as magnesium and potassium, both needed for photosynthesis.

If you have favorites in any of the above mentioned areas, protect them from serious damage by avoiding the materials that will result in the accumulation of salt. The salt will absorb the water instead of the plants. Be especially aware of areas with poor drainage, downhill of areas where salt materials are applied (roadways), and if you have unwittingly put in sensitive plant species, be sure to flush the area with plenty of fresh water in early spring or as soon as practical.

Salt sprays can also be damaging to plant parts they come in contact with. With evergreens, needles exposed to sprays absorb the salt and discolor and may even fall off. With deciduous plants, parts exposed to sprays lose their cold hardiness and are vulnerable to winter kill. In either case, plants exposed to sprays from roads or your own efforts from path clearing might best be protected with barriers of burlap, snow fencing, or some kind of screening.

I have noticed a fair number of red maple trees alongside a main corridor planted as part of a community beautification project. They are failing in the first few years after planting. I believe the main culprit is the accumulation of road salts in the root zones of the trees. Red maples are notoriously sensitive to salts in the soil, as are sugar maples and pin oaks.

Sugar maples formerly lined many of our roadways, especially when they were dirt roads for horse wagons and buggies. They fared wonderfully and were tapped each year for their delicious sap to be cooked down to produce our local syrup. As time went by, our roads became paved for more modern vehicles and subsequently were treated with all manor of deicing materials to make them safe for travel. Not only did the paved material stress the trees by denying the roots moisture and air, it also heated up in summer and added insult to injury by slowly cooking the poor roots. Then, the salts competed with the roots for moisture and ... well, look around any area where old sugar maples were roadside. Most are gone or in serious demise. It's just the way it happend.

For those who can afford it, there is a product that is touted as the very best available. It is known as CMA, short for calcium magnesium acetate. It is made from dolomitic limestone and acetic acid. It is largely benign to plants. Its cost, however, is twenty times the cost of rock salt, and that's when purchased by the ton.

A best bet for keeping both your plantings as well as human travelers safe around your home is to use some sensible substitutes with an additional step. Abrasive materials such as sand, sawdust, gravel, cinders, ground peanut or other shells, and kitty litter all work well when entries to homes are outfitted with a good boot brush mat. These are widely available, have stiff bristles, and are relatively inexpensive. Urea fertilizer is another material that can be used. A sensible and "safe for plants" mix would be 3 pounds of urea to 100 pounds of sand.

An additional pair of shoes or slippers inside the door is a bonus, and affords anyone the opportunity to clean the offending pair at a more leisurely pace. A hot cup of coffee, tea, or cocoa makes it all okay.

As for planning ahead, there are well established lists of salt-tolerant trees and shrubs, as well as lists of those species that are especially sensitive. These are based on extensive research and are very reliable.


From The Garden of Ed. Submitted for publication in The Towne Crier on November 17, 2004

© 2004 Ed Mues. All Rights Reserved.