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. So: does safe salt for trees exist?

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 mar­gins, 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.

While safe salt for trees does not exist, 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 has used potas­si­um chlo­ride on its side­walks. Cal­ci­um mag­ne­sium acetate is sup­pos­ed­ly the most plant-friend­ly. Select­ing a de-icing mate­r­i­al that is safe for pets is usu­al­ly a safe bet, and many stores are now car­ry­ing envi­ron­men­tal­ly-friend­ly ice melts. Just remem­ber, there is no safe salt for trees!

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