Plant-Safe Ice Melting Update: Pound Sand, Not Plants!
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Q. I have a stamped concrete walkway surrounded by a lot of mature foundation plants. The little research I've read suggests that I should not use Magnesium chloride, Calcium chloride or Potassium chloride because they degrade cement. Can you suggest another alternative? Play sand? Kitty Litter? I don't have access to wood ashes.
---John in Kensington, Maryland
A. I have gotten into lots of trouble in the past confusing 'concrete' with 'cement', so that was the first thing my poor dyslexic self went running to check. It's a little bit like "all pumpkins are squash, but not all squash are pumpkins". All concrete contains cement, but cement is not concrete; it's a combination of several ingredients, including interestingly, iron and aluminum. Cement can be used alone as a building material, but it isn't as durable as concrete, which is mostly crushed-up rocks and sand held together with cement.
So all concrete contains some cement, but often not a lot. Most of the material in concrete is the 'aggregate'—the crushed up stone and sand and such; the cement content may be as low as ten percent. Now if you're wondering why we've suddenly become "You Bet Your Building Materials", it's because warnings about what you can use on cement really don't apply to concrete, which is much more durable--and explains why MY stamped concrete patio hasn't been harmed by any of the three de-icing chemicals our listener mentions. (Neither have any of our nearby plants, which include one of my wife's best-producing peach trees and our nicest climbing rose.)
That's right: Calcium chloride, potassium chloride and magnesium chloride; I've used them all and have seen no negative effects on my adjacent plants or stamped concrete patio (which we really like by the way). When I realize that winter is about to hit, I buy a couple of shaker jugs of whichever of those 'alternative de-icers' I can find that doesn't also contain rock salt (a sneaky ingredient whose presence may be disguised by the use of its official initials: NACL). Rock salt really CAN harm nearby lawns and plants.
Then I always remember to follow the 'best practices' I learned years ago in an interview with Russ Alger, Director of the Institute of Snow Research at Michigan Tech University, where they receive an average of 25 FEET of Lake Effect snow every winter. If you KNOW you're going to get weather that will make surfaces icy—like freezing rain overnight—pre-treat your walkways with a little bit of de-icer before the event hits. Just a small amount will prevent ice from forming; then you can take that first step outside without falling on your keister the next morning.
If you're expecting real snow, then do like the song says and let it snow—and wait to apply any de-icer until all your shoveling is done. Don't toss any shoveled snow that may have been hit with road salt onto your lawn or plants, but DO toss clean snow onto them. Snow is a great insulator and plant protector; and the more clean snow, the more any de-icer that gets near your plants will be diluted.
My preference among the alternative de-icers? I'd have to say Calcium chloride, because it's the one I see for sale the most, and it works at the lowest temperature. But be assured that all three are much gentler on plants than rock salt, which people often choose because it seems to be less expensive. I say 'seems to be' because that low up-front cost doesn't take into account the long-term damage that the rock salt can cause to plants and surfaces. And you can melt the same amount of ice with so much less of an alternative that they wind up costing about the same. You just have to train yourself to use really small amounts.
OK—now what about 'play sand' and kitty litter?
I tried kitty litter once and it made a huge mess. But my good friend Howard Garrett, "The Dirt Doctor", who preaches the gospel of organics down in Texas, likes sand quite a bit. He says that the Texas Highway Department spreads something called "concrete sand" on their icy roads and it works very well and is totally non-pollutional. (If that's not an actual word, it should be.)
Anyway, for home use, Howard recommends 'lava sand' or 'granite sand', both of which, he notes, are nice little soil improvers—especially lava sand, which he really sings the praises of. Lava sand is sold in big bags as a soil amendment and for use in potting mixes; you should be able to find it at hipper garden centers.
For reliable info on what kind of regular sand homeowners should look for, and where 'play sand' fits in, I called Quickrete, the big national supplier of concrete, aggregates and sand. They were incredibly nice and helpful, and explained that "all purpose sand", the type you're most likely to find at big home stores, is the kind that's used to make icy surfaces safe. 'Play sand' is a more specialized product that's designed to be safer for kids to roll around in, but it de-slipperizes ice just as well.
Just be aware that if you're not careful, you'll track anything you use on your walkway into your house: salt, sand, whatever. That's why people who live in areas that get real winters need a boot scraper, a stiff-bristled mud room carpet, or to take their shoes off before they walk anywhere nice inside.