Scott LaFleur, Horticulture Director

It’s another wintery Monday morning at Garden in the Woods, and we have just finished clearing snow and making pathways passable. As part of our unending commitment to ecological gardening practice, we do not use any salt or calcium chloride on our paths and parking lot. We even request the town of Framingham exempt our section of Hemenway Road from salt use. Some of you may be asking "why?" and saying "I thought calcium chloride was the way to go." Here is the reasoning behind our decision.          

Common sense

We know that salt can have a wide variety of harmful effects on humans, and we are constantly told to cut down on our salt intake. It is not a very big leap to state that salt is not good for the environment in general and plants in particular. Rock salt, road salt, table salt, and calcium chloride—all technically salt—have negative impacts on plants. Plants are basically affected in two ways: first, through accumulation in soil and around plant roots; and second, through spraying or misting onto plant leaves, stems, and buds.  

When salt and water mix

To understand what happens to salt in the soil, think about when water gets into a salt shaker. The water is quickly absorbed; salt particles stick together and become as hard as a rock. The same applies to salt in the ground. When soil has excessive salt content, water is "locked up," making it unavailable to plant roots. This process can create a drought even in times of high moisture.

Sodium's harmful effects

You might think that heavily irrigating an area would wash away the salt. However, when salt mixes with water, the sodium and chloride ions separate. Chloride is then easily absorbed by plant roots and transported to the actively growing areas such as leaf margins and apical meristems. Chloride levels in these areas quickly reach toxic levels, which can lead to marginal scorch.

Sodium in the soil has two additional effects on how plants grow. The first (think back to the wet salt shaker) is sodium prevents soil from breaking into loose clumps. Instead, it binds large amounts of soil together tightly. This causes compaction and limits the amount of air and water available to plants, thus restricting their ability to grow. The second issue is sodium clogs the transport system used by plants to move micro-nutrients through the plant. This blocks other important micronutrients such as potassium and magnesium from entering the plant. The result is a high toxic level of sodium.

Spraying salt on plants can lead to a direct intake as salt works its way into gaps between cells.  This can compromise the viability of buds and shoots, which makes the plant very susceptible to the freeze thaw cycle they would normally be protected against. The high level of salt directly on the leaf surface is also toxic and can cause leaf burn and death of new shoots and twigs.  The overall health of plants is greatly affected, making the plants more susceptible to disease and insect problems.

Using calcium chloride?

Calcium chloride has been touted a better alternative to salt, but it can also be toxic to plants at high levels. In addition to being toxicity, calcium chloride is as listed on material safety data sheets as having the potential to cause severe respiratory and digestive tract irritation with possible burns; severe eye and skin irritation with possible burns; and cardiac disturbances to animals and people.

So what should you do?

Be prudent and use extremely small amounts of any deicing product. Better yet—just use sand! That is what we do at the Garden. Winter in New England means having to deal with ice. So, sand your walkways, give yourself some traction, and wait for a warm day when the sun and an ice chopper can do the work of many deicers. And stop using deicers in March! This is when plants are breaking dormancy and taking up a lot of fluid—and when they are most susceptible.

Finally, be aware of where snow will be piled and to where it will run off as it melts.