The effect of sea water on plant growth is an important inquiry for gardeners and landscapers near coastal areas, as well as for market and commercial farmers in regions of the world where irrigation water is scarce. Salt water generally has a deleterious effect on plant growth in most species; however some landscaping and ornamental plants and herbs are quite salt tolerant and will thrive when planted in locations that receive sea-water spray.
Sea water contains salt. Unless enough fresh water is also added to soil that has been saturated with sea water, salt will accumulate in the soil. The University of Wyoming Cooperative Extension explains that high salinity levels in the soil create an osmotic effect, in which moisture in the soil is less amenable to being absorbed by plant roots. The UW Extension also notes that plants can actually die of dehydration in moist soil if the salt content is too high. Drought-like wilting, stunted growth, and eventually plant death will result if the saline levels of water and soil are too high for any given plant.
Stunted Roots and Stems
A 2009 study published in the "Asian Journal of Crop Science" by researchers A Al-Busaidi, S. Al-Rawahy and M. Ahmed indicates that saline irrigation resulted in lower plant length and weight, as well as smaller root structures, in tomato plants compared to those watered with non-saline water sources. However, in field experiments conducted in Oman, where fresh water sources for irrigation are sparse, the researchers found that different tomato cultivars had varying degrees of saline tolerance. One particular cultivar, designated by the commercial moniker Number 38, was found to be particularly saline tolerant, with only minimal growth effects when irrigated with salt water.
Salt Spray Shear
Plants growing in coastal zones are affected by the spray of salt-water from waves and water-laden winds coming off the ocean. The plants that thrive closest to the shore are the most salt-tolerant, but, as the North Carolina Cooperative Extension describes, even these most sea-water-spray tolerant plants wind up growing skewed backwards from the waterfront as the sea water effectively shears off the windward side of the plant's foliage. The North Carolina Extension reminds landscapers and developers that when the protective "front line" of salt-tolerant plants is removed, this shear effect runs further inland, stunting the growth of less salt-tolerant plants that had been previously protected.