Dear Miss Floribunda,
You wrote about various kinds of salts in a column last summer, some of which are good for plants and others not. We’ve had several snowfalls this year, and I’ve seen trucks putting what looks like salt on our roads and alleyways. What kind of salt is it? Is it beneficial, or could it harm plants growing nearby, like the irises I have planted along my back alley? I once heard that the Romans used to put salt on the fields of the people they conquered to kill their crops. What salt was that?
Salt of the Earth on Emerson Street
Dear Salt of the Earth,
The mixture used on icy roads is based on sodium chloride (NaCl), which melts snow and ice quickly because it lowers the freezing point of water, but it can harm plants by inhibiting water intake and retention. This causes what’s called “physiological drought” within the plant. I doubt that enough salt was used this past winter to cause any significant problem, but I recall the blizzard of February of 2010, dubbed Snowmageddon. Hyattsville’s streets were deeply buried in snow. After a great deal of salting and plowing of roads, which left salt and snow above the curb line, real damage to some plants occurred. However, subsequent years of heavy rainfall have probably leached all of that salt out of the soil by this time. If you do have any doubt, you can have your soil tested at a number of laboratories. The University of Maryland Extension Service website lists laboratories to which you can send samples: extension.umd.edu/hgic/soils/soil-testing. It is always a good idea to have your soil tested periodically, anyway.
I referred your question about the Romans to my learned friend, Dr. Wordsworth Worterbuch. He knows the legend, which alludes to Rome’s crushing of its archrival Carthage. However, he assured me sodium chloride was far too precious a commodity in those days to have been so wantonly squandered. Roman soldiers were paid in salt, the Latin word for which is “sal,” and the word “salary” originates from this kind of payment — as does the expression concerning people who are or are not “worth their salt.” Dr. Worterbuch surmises that even were the soldiers ordered to salt any fields, they’d have managed to “salt away” most of it for themselves.
Getting back to Snowmageddon, its devastation of the creeping juniper along my curbside caused me to contact my Cousin Sally, who lives in the tiny town of Briny Beach, N.C. She informed me that coniferous evergreens are particularly sensitive to salt because they can’t get rid of it by shedding replaceable leaves, but drop their needles instead. Without any needles at all, they die. She advised me to dig up my junipers and plant something more salt tolerant in their place. Knowing soil in Briny Beach to be sandy, I asked her for recommendations for my clay soil. The salt-tolerant perennials she considered best for our area were daylilies, goldenrod, lamb’s ear, ice plants and other succulents. Sally also suggested creeping Jenny (Lysimachia nummularia), but she warned that it could become invasive. The goldenrod and lamb’s ear did well, but I replaced some of them later with plants I preferred. The daylilies thrived, and led to a near-addiction on my part, when I discovered the many beautiful varieties continuously being developed and learned how little care they need. For whatever reason, the ice plants did not long survive, but I found creeping Jenny to be a very easy and attractive low ground cover that spills prettily over curbs. It does tend to spread beyond the desired area, but is easy to pull out. The annuals she recommended — marigolds, cosmos, blanket flower and salvia — did very well indeed.
Spurred on by your irises question, I called Sally recently to ask about their reaction to salt. She characterizes irises as moderately tolerant of salt, and said that only heavy salt would permanently harm them. If you are worried about salt damage, she said, you could remove some of the soil around your irises and replace it with compost. Spring rain should finish the job for you if you have good drainage — and I assume you do, because irises won’t grow where drainage is not good.
To discuss this and other matters, please come to the next meeting of the Hyattsville Horticultural Society on Saturday, March 16, at the home of Dr. Julie Wolf and Corey Twyman at 4008 Hamilton Street. The meeting starts at 10 a.m. and will be followed by a seed germination workshop conducted by Dr. Wolf.