ROAD SALT AND TREES
What is the problem?
How can salt damage be recognized?
- Many trees--and shrubs--can be disfigured and killed by road
salt (sodium chloride), significantly raising tree costs for private and
public tree managers.
- The worst damage occurs to sensitive species planted near heavily
salted roads with high traffic, especially when they lie downhill, downwind,
or have poor drainage.
- Winter: look for "witch’s brooms" (cluster of twigs growing
out of branch ends) on deciduous trees, yellow tips on evergreen needles.
- Early Summer: look for marginal leaf scorch on deciduous
trees, yellow, brown, or fallen needles on evergreens--especially on the
side toward the road.
- Other problems can produce the same symptoms, so examine the whole
plant and site.
How does the damage occur?
Salt damage on sugar maple
Which common urban species are sensitive?
- Lower salt levels in the soil slow tree growth and vigor by
interfering with nutrient availability and uptake. Higher levels in
trees cause young plant tissues to dry out and die. In both cases,
the chloride ion is the active agent.
- Severe damage on evergreens comes primarily from spray taken up
by the needles.
- For deciduous trees, research suggests significant damage also
comes from salt being taken up by the roots and by soil structural collapse.
- The following common trees are usually severely damaged by road
- red maple (Acer rubrum)
- sugar maple (A. saccharum)
- hackberry (Celtis occidentalis)
- black walnut (Juglans nigra)
- Norway spruce (Picea abies)
- white spruce (P. glauca)
- white pine (Pinus strobus)
- Douglas fir (Pseudotsuga menziesii)
- pin oak (Quercus palustris)
What can I do about it?
- littleleaf linden (Tilia cordata)
Where can I get more information?
- Plant salt-tolerant species such as ashes, callery pears,
ginkgo, hawthorns, honeylocust, London plane, tolerant maples (Norway,
hedge, or sycamore), English and red oak, tolerant pines (Austrian, pitch,
or Japanese black), Sargent cherry, or Scholar Tree.
- Reduce salt application rates, lower the throwing distance, and
apply before roads freeze.
- Use a less harmful product such as CMA or IcebanTM, and mix in inert materials like sand.
- Raise the planting site, or block off the trees from the road
with a barrier.
- Improve drainage or adjust grade, so salt is easily leached away
- Flushing well-drained soils at the end of the winter, or incorporating
gypsum or a similar commercial product into the soil before winter begins,
has been found to reduce salt damage in some cases.
George Hudler, 1980. "Salt Injury to Roadside Plants," Cornell University
Information Bulletin 169. Most state extensions have available lists
of susceptible and tolerant plants. For other information, advice
and help on this topic, call offices of your State Urban Forestry Coordinator
or University Extension service, or visit urban forestry web sites.