Landscape
And
Nursery
Dialog
Mary Ann Rose
Commercial Landscape
& Nursery Specialist
The Ohio State UniversityJune, 1996
1996: A Banner Year for Salt Injury in the Landscape
Keywords: chemical injury, tree health, landscape, environmental problems/injury, weather
I t's pretty old news by now that the tough winter of 1996 left us a nasty legacy along the highways and byways of Ohio. Conifers have been particularly hard hit: spectacular salt injury to white pine, yew, and junipers has been evident close, and even not-so-close, to roads. In many instances, these plants appear to be killed outright, or as if torched on one side. So far, we've also observed significant bud kill in deciduous trees such as Callery pear and crabapple.
According to Rick Boyle of the Highway Management Department of ODOT, initial tallies of road salt usage in the state indicate that almost 50% more rock salt (sodium chloride) was used last year than during an average year. That amounted to more than half a million tons of salt! Furthermore this figure does not include how much salt/grit mixture, nor how much calcium chloride was applied in dry or liquid form to Ohio roads. Like sodium chloride, calcium chloride is a salt, but has a lower freezing point than sodium chloride. Of the two, sodium chloride is cheaper, but is more toxic to plants.
Rick Boyle also mentioned that about half of all of the salt used last year was used in Northeast Ohio alone. Just looking around at how bad the salt injury is here in central Ohio, I'd hate to imagine how bad it must be in NE Ohio!
Most of the injury we have seen is from wind-driven salt spray. When salt becomes airborne it can affect plants 100 to 150 feet from a highway, depending on the force and direction of winds. Classic symptoms of airborne salt spray appear on the side of the plant facing the road. This year whole plants were affected in many cases, and it seems likely that the higher doses of deicing salt coupled with driving winter winds are responsible.
Bud and branch dieback of deciduous plants from salt injury becomes apparent at budbreak, whereas damage on evergreens first appears in late winter, and worsens through the spring. Needles turn progressively brown from the tips towards the bases. The current understanding is that salt injury from airborne saltspray is caused primarily by cell and tissue sensitivity to the chloride ion. Salts that accumulate on the stems and buds also cause desiccation of those tissues by drawing water out of them.
A lesser problem associated with road salt usage is soil contamination. In fact, the Romans picked up on this a few thousand years ago! Salt must have been cheap then, too, because they found it was a handy substance to wipe out agriculture in any uncooperative civilization raising a fuss about being conquered. Any type of salt (including fertilizer, which is salt) has the potential to raise the osmotic potential of soil solution to a point that roots
no longer can take up water and nutrients. Roots in essence experience a drought in excessively saline (salty) soils even when moisture is available. Rhododendrons and azaleas are particularly sensitive to this kind of injury.
Salts in soil solution also may have a direct effect on leaves if they are taken up by the roots. Sodium and chloride ions can move through the plant and accumulate in toxic concentrations in the leaves. Leaves affected in this manner often appear burned along the margins or leaf tips.
So what can we do about salt injury? Driving along SR 33 East I noticed a half-dead field of eastern white pine right next to a healthy field of spruce. It seems to me that using alternatives to white pine, taxus, and juniper along busy roads might be advisable. Or at least be aware that extensive injury is a possibility in years like 1996. Plants that the textbooks tell us are supposed to be sensitive to salt, in addition to the above, include beech, river birch, boxwood, black cherry, cornelian cherry, cotoneaster, flowering dogwood, Douglas-fir, white fir, sweet gum, forsythia, hemlock, hickory, American holly, common lilac, red and sugar maple, flowering plum, quince, serviceberry, white spruce, sycamore, and tulip tree. Salt-tolerant species include honeylocust, horsechestnut, oak, Austrian and mugho pine, Colorado spruce, Norway maple, potentilla, bayberry, and evergreen euonymus.
A barrier of some sort between the road and and ornamental planting also may prevent salt deposition on foliage. Even rinsing the foliage might be recommended to the homeowner, but this isn't an easy proposition in the winter time. Where salt contamination of soil is suspected, leaching the soil by irrigating heavily can help. Heavy spring rains will accomplish this.
On the bright side: maybe landscapers who have been rained-out all spring may get some good business this summer replacing road-side plantings!
