University of Maryland Extension

What a Cold Winter Vortex Has Wrought (2014)

Stanton Gill, Extension Specialist, IPM and Entomology for Greenhouses, Landscapes and Nurseries
Sweet gum ball in snow

Recent Weather
A hot, dry California, a wet, cold England, a warm Alaska, and a cold central Florida - what a wild winter America and Europe have experienced this year! Why? Because of something called a shifted ‘polar vortex’. Before this winter, most people never heard of a polar vortex. The polar vortex, which is normally tucked away much closer to the Arctic, has swept down several times this winter, bringing cold temperatures and snow to large segments of the U.S. east of the Rocky mountains. Florida has seen several periods of freezing temperature dips this winter and Georgia was caught completely off-guard in late January with snow and cold temperatures. The news media published pictures of cars sliding off roadways in Georgia with 2 – 3” of snow. There were major shortages of road salt in the south by the end of January.

Contrast this weather to the summer of 2013 which was the fourth-hottest year on record. Meteorologists have been predicting we will have wild weather pattern swings and more violent weather. It looks like they were right on the money. Why are we having a colder than normal winter? The polar vortex has been pulled south by an unusually extreme jet stream, which some scientists have suggested will happen more frequently in a warming world. This shift also has an impact up north which results in the far north being much warmer than normal.

Alaskans are used to cold winters, not warm winters. In Alaska there is a major roadway called Richardson Highway that runs to the port city, Valdez. This winter the roadway suffered a series of avalanches that buried the road 40 feet deep in January 2014. While the winter temperatures have been really cold down in the lower 48 states. It has been really warm in Alaska where instead of snow it started to rain in January. Temperatures at the tops of the mountains were approaching high 40s, even 50 degrees, and the rain destabilized the snowpack that is there every year resulting in incredible snow slides. Even England was impacted with this weather shift. Winters in England are usually cold and misty with a lot of cloud cover. This winter has had record-setting periods of heavy rain. In California, this weather pattern is resulting in an extended drought there with Governor Jerry Brown declaring a drought emergency. This year is actually the third year of major drought in California.

The mid-western part of the United States suffered temperatures in the sub-zero range for extended periods of time. Grape growers and apples growers in the Mid-West have reported major damage on bud wood in orchards and vineyards. Temperatures fell to unprecedented levels, and consequently, low temperature records were broken across the U.S., leading to business, school, and road closures, as well as mass flight cancellations. Fuel prices reached all-time highs. People receiving their heating bills in February were stunned. There were shortages of wood stove pellets and firewood prices climbed upward in February. In late January and early February, several restaurants reported reduced customer traffic because people apparently did not want to go out in the extreme cold. Is this sounding like a disaster movie?

De-icing Salts Used Heavily This Winter
Record amounts of de-icing salts were applied to roadways and sidewalks. Many landscape companies started the winter using the plant-safe, de-icing salts such as calcium chloride. As the cold periods continued, the calcium chloride supplies dried up and many people applied sodium chloride which is much more damaging to plants. Some landscape companies found supplies of potassium chloride in the south that they started using in February to keep the ice in check. On visiting one of the big box stores I found they had moved water softener salt to the front of the store to sell to customers to melt ice on their home sidewalks and driveways. This material is good old sodium chloride. Several landscapers told me the price in the beginning of the winter was $4 for 50 lbs of sodium chloride and by February the price had jumped to $9 per 50 pound bag.

The highway departments in Maryland reported by the end of January they had applied over 280,000 tons of salts to Maryland highways. Cars were caked in a fine white powder that persisted for weeks on end. This has been good news for car wash businesses who have been doing brisk business this winter. It was a great photo opportunity to shoot pictures of plant material covered with salt residues that looked like decorative snow flocking. We should mention that road de-icers often consist of both salt and sand, with the salt component consisting mostly (98.5 percent) of common sodium chloride with traces of other mineral salts. (See Melting Ice Safely, FS 707)

I could not find accurate figures of how much salt went down on sidewalks and parking lots but it was a lot. The worst part has been that this extended winter cold required repeated applications, sometimes 3 or 4 times a week, in January and February. Purdue University reports that nationwide each year, more than 15 million tons is applied to de-ice sidewalks, walkways, and driveways.

There is an enticing book published titled “Salt” that reviews the history of salt in modern society. I know it sounds deadly boring, but the book is a delight to read. Salt for centuries was the essential material to preserve food and used as an important food spice. Nations went to war over ownership of lands rich in harvestable salts. Many cities were established near salt mines to supply this valuable mineral. Salt, in ancient societies, was the equivalent in importance of oil and other fossil fuels, in our current societies.  It is rather humorous to think we now use salt to keep us mobile in our modern societies.

The benefits of using salt to prevent cars from sliding and people slipping cannot be denied. The salt use also has a darker side – it is not beneficial to plant material. Salt’s toxic impact on plants has been known since ancient times when it was used for biological warfare to destroy an enemy’s fields and crops.

Tons of salt have been applied to area roadways. Look for damage on
trees and shrubs later in the season.

Why Are Salts Toxic to Plants?
Calcium chloride (melts ice down to -25 °F) and potassium chloride (melts ice down to 12 °F) do the least damage to plants, but the chloride can cause some damage to plants. The most commonly used salt, because of its low cost, is sodium chloride. When sodium chloride dissolves in water, the sodium and chloride ions separate. When this happens, the sodium ions in the salt replace the other nutrients in the soil that plants need (potassium, calcium, and magnesium), so these nutrients are unavailable to the plant. When this occurs, plants may develop deficiency symptoms, particularly those associated with potassium deficiency. Salt also absorbs the water that would normally be available to roots, which dehydrates the roots, changes their physiology, and causes additional plant stress. Roots absorb the chloride ions and transport them to the leaves, where they accumulate and interfere with chlorophyll production and photosynthesis.

An alternative de-icing product that does little detectable damage to plants is calcium magnesium acetate (CMA), a salt-free melting agent made from limestone and acetic acid. It is effective in melting salt down to 0 °Fahrenheit. It cost more, so the lesser expensive materials are used on most highways and sidewalks. It is probably a good idea to stock up on this material for upcoming years.

It is often difficult to diagnose salt damage on deciduous trees and shrubs while plants are still dormant. Unfortunately, damage symptoms show up later in the spring and early summer. Usually, leaf buds facing the road are killed or are very slow to break dormancy and bud and leaf out in spring. Flower buds facing the road or sidewalk often fail, but the unaffected side of the tree or shrub flowers normally.  Plants such as maples, redbuds, hornbeams, dogwoods, beech, crabapples, sycamore and London plane, cherry, oaks and shadbush are very sensitive to salt damage. In evergreens, damage usually appears in late winter as needle browning that starts at the tips. White pines are very sensitive to high salt levels. White pine plantings have been growing in popularity in the last 10 years and many are planted near roadways where salts splash into root zones.

In March you can take soil samples and check the soils for salt levels. Sample areas near parking lots plants and near sidewalks where runoff of the salts is likely to occur.

Salts Happens – So What Can You Do for Your Customers?
Additives to the soil such as organic matter, activated charcoal, and gypsum can help with rectifying soil salinity problems. However, these are not quick fixes and if the salinity levels are extremely high, no amendments will reverse the situation. All additives, regardless of the material used, need to be incorporated into the soil, usually in the root zone. This need to incorporate the amendment is one of the limiting factors in using soil additives to mediate salt problems. Although a few reports suggest surface applications can be helpful (particularly for gypsum), the general consensus is that the additives need to be fully incorporated into the soil in order to be effective. Since plants growing in soils rich in organic matter show increased tolerance to salt, a program to increase organic matter in areas prone to road salt is a good preventative plan.

Gypsum (CaSO4• 2H2O) is the most common additive used to counter salinity problems associated with sodium chloride. Gypsum separates into calcium and sulfate in the soil. The sulfate forms sulfuric acid in the soil and helps to neutralize any effect that calcium may have in raising the soil pH. The calcium replaces the sodium on the cation exchange sites. The sodium and sulfate form sodium sulfate (NaSO4) which is a product that can be leached from the soil with water. Rates for gypsum applications depend on the salinity of the soil. However, rates in the range from 10 – 50 lb per 100 sq ft of root zone of the plant.

How About Cold Injury?
The temperatures in January and early February dipped several times to the single digit range. Plant material that was at the edge of the hardiness zone will likely show injury this spring.  We would suspect that many crape myrtles will suffer branch dieback, but generally the root systems should survive. Many homeowners planted figs into landscapes and they can expect branches to die back from the cold temperatures. Nandina and Chinese holly will likely suffer scorched foliage and dieback. Cryptomeria may show some scorching from the low temperatures.

Much of the winter cold injury will show up as plants start breaking dormancy this spring and memories being short lived for many, people will puzzle over why plants are showing dieback this spring. Spring will be soon here and most people will be glad to move out of the polar vortex and into more pleasant weather. (See Winter Damage on Landscape Plants, HGIC article)

Crape myrtle covered in ice on February 5, 2014. This spring, look for winter
injury such as dieback on plants in the landscape.
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