Trees vs. Salt

Each year, winter brings cold weather, snow, ice, and dormancy to our trees. Here at Tree Pittsburgh, our tree care activities slow down (though we still host pruning workshops, as it's the most ideal time of the year to prune). Insect and disease pests are dead or dormant for the season. In the winter, a larger threat to dormant trees emerges. It attacks healthy trees as well as sick trees, large trees as well as small ones. This winter time threat? De-icing salt.

In small quantities, salt makes our food taste better and does a fine job of melting ice on our streets and sidewalks. Usually, trees can handle small amounts of salt and spring rains help to wash salt away from the soil and tree roots. But, when too much salt is applied, it can build up in the soil and start to desiccate (make extremely dry) and destroy tree roots. You can see this in the spring in a few ways: either when a tree leafs out and the edges of the leaves have brown margines, or when the tree fails to leaf out at all because it died from too much salt. 

Not only will salt hurt the trees, but over time too much salt can begin to destroy soil structure which can create soils where nothing will grow. Salt spray from fast-moving traffic can also land on branches and buds, causing desiccation and damage. Each tree species has a different level of tolerance to salt. Trees native to coastal areas usually have higher tolerances, as they have evolved close to the ocean and the high salt levels.

There are a number of things that can be done to protect trees:

  1. Plant the right tree in the right place, since some species are more salt-tolerant than others. Just remember: no tree is salt proof!
  2. Clear as much snow and ice as possible before salting, and use it conservatively.
  3. After thawing, sweep up any remaining salt and save it to re-use later.
  4. When spring arrives, water trees that have been exposed to a lot of salt. This will help to wash the salt from the soil.
  5. Consider an ice melt alternative.

There are many alternatives to salt. Calcium chloride is slightly less damaging to plants, when applied correctly. Phipps Conservatory used potassium chloride on its sidewalks. Calcium magnesium acetate is supposedly the most plant-friendly.

No matter what product you use, remember to use it conservatively and take care of your trees!

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