It’s winter, and that means snow and ice on the sidewalks and paths. Most people use a de-icing product at least some of the time, but what do those products do to your garden? All de-icing products have an effect on plant life, whether you see it right away or not, but some types are harder on plants than others. And they don’t have to soak down to the roots to do damage- ever notice evergreens along the road that are brown and burnt looking at the height where throw from the road plow hits them? That’s from the de-icer mixed with the snow hitting them.
The cheapest de-icer is good old sodium chloride- rock salt, table salt. This is the cheapest de-icer, which is why it’s used on roads so much, despite the harsh effects on car bodies and bridges. It is effective down to 12 F degrees, but is the hardest chemical on plants. It also breaks down concrete and rusts steel and iron. When it washes down into the soil, it can keep the water in suspension, so that the plants cannot take the water up and they dry out. Not recommended for home use!
Potassium chloride de-icer, also used in fertilizer and as a sodium substitute by people with sodium sensitive high blood pressure, is as effective as sodium chloride, but is even more damaging to plants.
Calcium chloride is the most commonly used household de-icer. It works all the way down to minus 25 degrees F and works quickly. But excessive use can hurt plant roots, and it combines with the melted ice to form a slimy solution that makes walks and steps very slippery.
Magnesium chloride is only good down to 5 degrees F, and it is also harmful to plants in large amounts.
Outside of the chloride family, we have urea, which is mainly used as a nitrogen source in fertilizer. Urea is good down to 21 degrees F, is much less damaging to metal and concrete, and does less damage to plant life than potassium chloride does. The draw back is that it, like most nitrogen compounds, can contaminate water supplies, even deep ones.
A newer de-icing compound is calcium magnesium acetate. Made from dolomitic limestone and acetic acid (vinegar), it doesn’t damage concrete and has very little effect on plants. Of course, it has some draw backs: it’s only good down to 20 degrees F and it’s a lot more expensive than other de-icers. It works differently from most other de-icers; rather than melting the ice and creating a solution, it keeps snow particles from sticking to each other and forming ice, and from sticking to hard surfaces.
A product called Safe Paw is salt (chloride) free, and claims to be safe for plant life and animals, who get de-icer on their paws, where it can burn or where they can lick and ingest it. It is also supposed to be nondamaging to concrete and wood. While it sounds ideal, it is very expensive. I cannot find what it is actually made of.
Remember that de-icers are just what the name says- they work on ice, not snow. Snow is too loosely packed for de-icer to work well on, and it would take a tremendous amount of the product to remove snow. De-icer works best on thin layers of ice. If at all possible, shovel soon after snow falls before it has time to get walked or driven on and compacted.
Also bear in mind that de-icer does nothing for traction- in fact, the layer of brine (water and salt) on top of the ice can actually make it slipperier. Sand, clay kitty litter (NOT the clumping kind!), cracked corn or bird seed all work as skid proofing and won’t hurt your garden or walkways. Do not use cracked corn or bird see if you are using a de-icer or the birds will be eating the chemical along with the bird food. Of course, anything you use on the walk will end up in your house to some degree- but that goes for de-icers that can harm pets as well as traction products. Use de-icing compounds as judiciously as any other chemical.