Salt in Coastal Gardens:
At the end of the Punic Wars (264-146 BC) the Romans destroyed the great Phoenician city of Carthage and burned it to the ground. After a century of war, the Romans wanted to be sure Carthage would never rise again. It was rumored that Rome sowed the entire city with salt so that there would be no chance of anything growing again.
Salt. We are surrounded by it here in Ocean Shores. It is in the air as well as the soil. Many say that salt is the reason that fresh, marine, coastal air is so healthy. Although I have not been able to confirm that in physiology research journals, our air out here does smell and feel great.
About plants – if one could salt an entire city would plants truly not grow? What does salt do to plants? Salt in the air can burn leaves or dry them out until they prematurely drop off. This is especially the case when it is windy; something we see often here. About the only thing you can do is try to protect plants from the salty wind, by placing them behind fences or buildings to act as windbreaks.
Anyone who has gotten through beginning biology has heard of osmosis – the process where higher concentrations of salt draw water across a membrane towards it. Too much salt in the soil will draw water out of plant root systems, thus drying out the whole plant. Since plants absorb most of their nutrients dissolved in water through their roots, too much soil salt can deprive plants of the nutrients they need to grow and mature. Excessive salt changes the biochemistry of the plant and interferes with its normal metabolism. Yes, salt does make a plant’s life difficult, but not impossible.
So, what is our soil like? Our native soil is a mostly sand with some dust-like silt. Although not quite sterile, it contains few plant nutrients. Our soil drains readily because of the sand and high winter rainfall. Although our yearly rainfall amount varies quite a bit year to year, we get at least twice as much as Seattle’s 37 yearly inches. (See Ocean Shores monthly rainfall data submitted by the Coastal Interpretive Center usually published in this paper.) The fast and thorough drainage also lowers the soil pH, making our soil slightly acidic.
So, what about the salt content? Regular salt is a combination of sodium and chloride (NaCl.) Sea salt also contains significant amounts of magnesium, calcium, phosphorus, potassium and minor amounts of iron, all nutrients plants need. Too much sodium and chloride are the major the problem. Drainage becomes the significant factor. Most garden soil specialists note that it takes at least 20 inches of rain a year in well-drained soil to remove excesses of NaCl. We have three to four times that much. So that explains the lack of concern about salt in Ocean Shores soil. Salt from the ocean does invade both our air and our soil. However, the freshwater rains quickly carry the salt through our soil before it has a chance to severely impact our plant life, most of the year.
Plants here do have to cope with soil that is on the acid side, lacking a comfortable amount of nutrients, and having a lot of water draining through. Salt is still in the air and remains long enough in the soil to make salt tolerance a positive characteristic. Most of our native plants are somewhat salt tolerant, do not require a high amount of nutrients and are able to survive changing water availability to make it through our wet winters and dry summers. Our wax myrtle, blueberry, willow, and salal are good examples.
If you’re looking to plant others, select plants that are first on deer resistant lists and then look for salt tolerance, plants not needing a lot of nutrients, those that prefer acid soils and are adaptable to varying water conditions. Shore pines and some of the spruces are reasonable trees to try. For perennials you might try thyme, lavender and other herbs, barberry, juniper, yucca, shasta daisies, sea thrift, ajuga or rudebeckia.
You can also add organic matter (compost) to your soil. Adding calcium will help balance out extra salt as well as increase nitrogen, phosphorus, and potassium absorption. Adding lime will sweeten the soil making it less acid. Watering deeply during the summer growing season will help keep extra salt washed away. These measures will give you the possibility of a greater variety of plants.
This article was originally printed in The Ocean Observer, January 2019.
