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How to Avoid Salt Damage to Trees

Snowfall seems to have happened very late all across the country this winter, but now that it’s here, most people are trying to find ways to get rid of it. But salt, while effective for deicing roads and streets, can have extremely detrimental effects on trees, causing things such as necrosis, burned tips, or failure to bud entirely. Remember that salt damage can happen in two ways — either through contaminated soil or through salt spray (atomized particles in the air).

Here are some things to remember to try to minimize the damage.

For roadway/sidewalk trees where contaminated soil is likely:

  • Trees that are adjacent (< 15 feet) to roadways are likely to suffer the worst damage
  • Trees on downhill areas are more severely affected that those on uphill areas
  • Trees in depressions or with settlement around their trunks are at greater risk that trees in raised sites

For high-speed roads where salt spray is likely:

  • Trees on the downwind side are at the greatest risk of injury
  • Affected areas tend to be on the side of the tree facing the road
  • Trees sheltered by fencing or other barriers suffer less damage
  • Injury is greatest on the lower branches
  • Flowers may fail to bloom, or fall prematurely, on salt-contaminated buds

Our recommendations for reducing salt-related damage to trees, made directly by James Urban, FASLA, are as follows.

1. Use magnesium chloride in the early and late parts of the winter when temperatures are above 5° F (-15° C).

2. When temperatures are predicted to be below -5° F (-15° C) use calcium chloride.

3. Use liquid forms of each chemical.

4. Educate maintenance personnel on proper techniques to reduce application rates.

5. Flush the sidewalks, beds and water harvesting system each spring after the last ice event and before the plants bud out.  Wash the canopy of trees at this time.

6. Using larger quantities of well drained soil (at least 0.75″/1.9 cm per hour) will reduce the impact of water born salt on the tree. A minimum of 500 cubic feet (14 cubic meters) with 1,000 – 1,500 cubic feet (28 – 42 cubic meters) preferred, will significantly reduce the impact of water born salt by giving the tree a large buffer against salt concentration.

7. For trees planted in areas of poorly draining subsoils (less than 0.25″/.6 per hour) install subsoil drain lines when planting the tree or improve the drainage rates of the subsoil by loosening the compaction in the subsoil. The combination of larger soil volumes and better drainage allows salt to be flushed through the soil by spring rains.

For more information, read our original blog post about minimizing the effects of salting on urban trees or read Forest Research’s “De-icing salt damage to trees” report.

Image: BFW

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