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Plant-Safe Ice Melting

How to Protect Your Plants When You Melt Sidewalk Ice

Yes, its that time of year, when most of us have to deal with snow and ice. And for as long as I've been in this business, gardeners have been asking me: "What's the safest thing we can use to melt ice on walkways near our gardens, lawns and other plantings?"

And so, this week's show (, features an interview with Russ Alger, Director of the Keweenaw Research Center and the affiliated Institute of Snow Research at Michigan Tech University (, right on the shores of Lake Superior; where, Russ reports, they receive an average of 25 FEET of Lake Effect snow every winter!

We knew we'd get a lot of questions about the interview, so we're turning this Question of the Week into a Special Report on plant-safer de-icing options—based on our interview with Russ (including some edited-for-time parts you won't hear on the actual show), some leads he provided, a TON of research dug up by YBYG's fearless fact-finding fanatic, Charles Younger (take a bow, Chuck!), and some basics I've learned over the years. Here we go:

  1. Keep deicing chemicals physically away from your plants.
Russ' first suggestion is to divert the runoff from whatever product you choose to use away from your planted areas. "Make a little gravel drain between your walkway and planted areas," he explains, " so that any runoff is channeled to the nearest sewer system or drain." (A larger scale, swale-like variation of this technique might prove helpful to folks with plantings close to roads deiced by local highway crews.) And never toss shoveled snow or ice from treated areas onto planted areas—always move this contaminated material to where plows or drains can take it away.

  2. Whatever you use, use less.
There seems to be a clear consensus that—as with lawn and garden chemicals—homeowners use too much chemical deicer. "You just need to get the melting process started", explains Russ. "Use a small amount to start, and wait till it's all dissolved to add any more. Keep adding small amounts and you'll achieve maximum melt with a minimum of chemical." And, of course, be sure you remove all the snow on top before you apply anything; reserve your deicer use for the thin patches of ice left behind on the surface of walkways.

  3. Pre Apply.
Don't wait until the snow event is over to start deicing your walkway. As soon as it starts to snow or sleet (or even a little in advance if you're certain its going to happen), spread a small amount of your deicer of choice on the surface you want to keep ice-free. This is called "anti-icing", and its VERY effective. "You get a little bit of melt right at the surface when you pre-apply", explains Russ, "and even a very small amount of chemical will then prevent that area from freezing."

  4. Think liquid.
In anti-icing, solid chemicals can blow away or be tracked inside while you're waiting for the snow or sleet to show up. Liquids move around less—and are also just plain more effective than the same chemicals in solid form. On the Federal Highways website many states report cutting their salt use dramatically by spraying a liquid saltwater brine on roads before a snow event occurs. Washington and Oregon report similar success using much less corrosive Magnesium chloride—and Boulder's report even gives the percentages they use to create their de-icing mix: 30% magnesium chloride and 70% water.

Although Russ feels that they will eventually become very popular, liquid deicers aren't all that available to homeowners yet. In the meantime, he says you can make your own—just combine the chemical of your choice with enough hot water to completely dissolve the solids. (Thanks to Boulder we even have a recipe—a little more than two parts water to each part magnesium chloride should make a fine liquid deicer.) Then apply the liquid to the surface with a pressurized sprayer. Just be aware that some corrosion of the sprayer's parts will occur right away with salt, and may also eventually occur with less corrosive materials; specialized brass fittings will limit this problem.

Or try something I did last year; mix up half a bucketful of solution (I used calcium chloride because that's what I had handy) and slosh it slowly and carefully onto the sidewalk so that any extra drains away from your plants. It was VERY easy to do, and worked great—no ice at all the next morning! (Just don't let it sit too long in the bucket—liquid calcium chloride generates an astonishing amount of heat.)

  5. Don't do anything if it's TOO cold out.
Russ explains that rock salt is good at melting ice down to around 15° F. Calcium chloride works at the coldest temperatures—down to 5° F. Potassium and magnesium chlorides are in the middle. If it drops below 5°, don't use anything; Russ explains that it just won't work unless you use extreme amounts. If it gets that cold and you haven't pre-applied, wait until the weather warms up to apply your ice melter. If its really treacherous and the temperature is going to stay low, spread some sand for traction while you wait.

  • If you can do it without damaging the surface you're clearing, physical removal of the ice—chopping and chipping with a dedicated ice removal tool—is the safest for your plants. Propane burners—like the weed killing torches I love so much—will also do the job safely, but they can take a long time and use a lot of fuel. (And any melted water you can't sweep away will refreeze.)

  • If you're going to use chemicals, pre-apply them to the surface before the snow or sleet arrives, in liquid form if possible.

  • No matter what, don't spread chemicals on top of snow. Remove all the snow, then apply your ice melt to any thin layers of ice that resist shoveling. Shovel promptly after a snowfall, and work from your doorway out; a lot of problem ice is created when people walk on top of snow and pack it down.

  • Use trenches to divert runoff. Dump contaminated snow and ice in non-planted areas.

  • Salt is popular as an ice melter because it is abundant and cheap; it is the most corrosive choice and poses the most danger to plants and soils.

  • Potassium, magnesium and calcium chlorides are more expensive; but you use so much less that the cost differential may not be that great in the long run. They're readily available, and are much less corrosive to surfaces and kinder to plants.

  • Potassium chloride is a good choice for warmer areas; plants can handle a lot of potassium—its one of the three main plant nutrients. But it's not effective at very low temperatures.

  • At least according to Federal Highway websites, Magnesium chloride seems to be the most popular alternative to salt that's being used on a wide scale right now. It's certainly less corrosive, and plants do need small amounts of magnesium; just don't use more than necessary.

  • In really cold areas, calcium chloride would seem to be the best choice. It's the most effective at cold temperatures, and calcium is a nutrient that plants can take in fairly large quantities—in fact, it's the nutrient most often lacking in large amounts in American soils. But don't go overboard—this substance generates a lot of heat when it goes into solution.
And of course, there's lots of really neat things on the horizon. Look for liquid pre-icing sprays to become more available to homeowners, and for contractors to begin offering 'smart pavement' technology—where concrete is sprayed with a special epoxy coating that's then treated to act like a sponge, absorbing and holding small amounts of ice melting chemicals in its surface until they're needed.

Here are some links to explore if you'd like to learn more:

Institute of Snow Research De-Icing Page:

Detailed deicing information using Magnesium chloride from Boulder:
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Liquid deicing reports (mostly saltwater; some magnesium chloride) from other states: ct.htm

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