In this season of ice and snow, pause to think of the flowers of spring. Plants that live near paving, including turf grass, are in jeopardy from the ice-melting chemicals that have become the other "white stuff" of the winter landscape.
Plants are damaged in two ways by the chemicals: Salt-laced snow and slush burns evergreen foliage and latent buds. Moreover, salt in the soil can prevent roots from absorbing water and nutrients and affects the long-term health of both evergreen and deciduous plants, including ground covers, spring bulbs and lawns.
The symptoms include distorted and stunted growth, branch dieback, lack of flowering, and leaves with browned margins. Salt contamination also can cause stress that invites diseases and pests — assuming the afflicted plants live.
David Yost, a plant specialist at Merrifield Garden Center, remembers seeing a hedge of yews killed outright by a salt-contaminated snow pile shoved to a corner of a parking lot. "Roots and all," he said.
Fortunately, paths can be cleared without maiming your landscape, using alternative products and some care. More than your plants are at stake: Excessive salting poses a risk to pets, damages masonry and automobiles, and can add to the pollution of the Chesapeake Bay.
The most damaging type of thawing agent — rock salt, or sodium chloride — is also the cheapest and most readily available. Protecting your landscape may mean having to shop around to find something other than rock salt.
Some gardeners have relied on urea, which doubles as a nitrogen fertilizer, the theory being that it fed plants as it was washed by rain into the soil. But environmentalists frown on the substance for its capacity to pollute waterways. "We need to be concerned about the additional nitrogen added to the nutrient load in the bay," said Mitch Baker of American Plant Food Co., the Bethesda-based independent garden center.
He recommends a lower-impact salt called potassium chloride, which is not as fast-acting and is most useful down to only 20 degrees, but is kinder to plants and concrete. He sells a product called Melt-A-Way made by Jonathan Green. A 20 lb bag costs $11.99.
A common ice-melting chemical, calcium chloride, works at far lower temperatures than the others but produces a greasy film and is highly damaging to concrete. It is also not much kinder to plants than rock salt.
Yost said his garden center sells a product called Mag, which contains magnesium chloride. It is effective at sub-zero temperatures and is less corrosive to masonry and plants than the others. The drawback? Small, convenient bags are hard to come by. Merrifield sells it in 50 lb bags for $24.99.
"It's effective to very low temperatures, and it's essentially noncorrosive," Yost said.
Recently, different types of de-icers have been developed for consumers that are not salt-based and won't damage plants or soils, according to their manufacturers. One is named IceClear, sold as a liquid and meant to be sprayed on surfaces before storms arrive. This forward-thinking approach, incidentally, makes all de-icers more efficient and reduces the quantity of product needed — key to minimizing plant damage.
IceClear is sold in gallon jugs and designed to be used in a garden sprayer. It is made from corn extract and a chemical called potassium acetate, said Tom Thomson of Monterey Lawn and Garden Products in Fresno, Calif., the manufacturer. The product sells for $20, which should provide two applications for an area of 1,000 square feet, he said.
A company named GAIA Enterprises in Richboro, Pa., has developed an ice-melting product that it says is far safer for pets than conventional salts. Dogs can get rock salt lodged in their paws. Indoors, it heats up and irritates the animal, which licks it and ingests harmful salt, said spokesman John Eccleston. Safe Paw is made with a chemical compound called an amide, infused with glycols. It is available at pet stores, where it sells for $14.95 - $19.95 for an 8 lb container.
Sometimes, the salt damage to the landscape is out of the resident's control: Street trees and garden beds close to a highway served by snowplows often suffer salt damage from the spray kicked up from passing cars. The mist routinely carries 10 to 15 feet from the road, said Adria Bordas, horticultural extension agent for Fairfax County. She often sees damage to evergreen screens such as arborvitae, Japanese cedars and white pines.
Phil Normandy, curator of plants at Brookside Gardens in Wheaton, thinks of the country roads in New England that have become commuter thoroughfares and are now routinely salted. The roadside sugar maples, which are particularly sensitive to salt damage, die one by one.
The Maryland State Highway Administration, for example, spreads on average 236,000 tons of rock salt each winter, said spokesman David Buck.
Bordas advises residents to spray plants that have been salted with water. This requires a mild winter's day and the trouble of taking a garden hose out of winter storage. Contaminated beds should be given several soakings. The poorer the drainage, the more likely salts have built up and the harder they are to wash out. Ironically, the salts harden the soil and reduce its internal drainage.
"If you're going to use ice-melting products," said Bordas, "use them sparingly." And before the storm arrives.
©2005 The Washington Post Company