The following are some of the issues affecting coastal gardens:
1) Salinity – Sea water contains less dissolved minerals than fresh ocean water.
Therefore seawater tends to have a higher salinity level than freshwater or saltwater lakes. Salt levels may reach up to 15 parts per thousand (ppt). Freshwater is usually around 1 ppm, while saltwater lakes range from 0-2 ppm.
Salinity affects all types of plants. However, it is most significant for marine plants because they need high concentrations of salts to survive. Salts can cause plant death if not removed properly. For example, when salt levels exceed 30 ppm, the roots become stunted and die off; the leaves turn yellow and drop prematurely; and the fruit becomes shriveled and dry.
In addition, seawater is corrosive to metals such as copper and zinc. Copper and zinc corrode at temperatures above 100°C (212°F), so seawater will damage metal pots. When these metals touch seawater, they react with each other causing rusting and corrosion. If left untreated, seawater can cause lead poisoning in children who drink contaminated water.
2) Temperature – Sea water’s temperature varies considerably depending on location along the coastlines of the world.
In the northern hemisphere, the water’s temperature is lowest in January and highest in July. In the southern hemisphere, these temperatures are reversed. The ocean’s temperature also varies considerably with depth. The average surface temperature of the ocean, for example, may be 28°C (82.4°F).
Yet at a depth of only 10 metres (33 feet), this temperature drops to only 20°C (68°F). Even greater drops occur at greater depths. These temperature variations can severely affect plants and animals living near the oceans.
Along coasts with moderate or cold climates, water temperatures rarely exceed 10°C (50°F) for extended periods of time. Many crops from the Mediterranean region, like olives and cherries, cannot survive in such areas. Olive trees cannot survive even a few days of temperatures below 10°C (50°F). Many plant nurseries in such locations grow Mediterranean crops in greenhouses to protect them from difficult climate conditions.
Greenhouses are also used to extend the growing season into winter to take advantage of available soil nutrients and water.
Along coasts with warm climates, water temperature is rarely below 20°C (68°F). In such areas, plants must endure hot temperatures throughout the summer months. Some plants like rose bushes have heat tolerant structures like thorns to help protect them from animals and insects that may harm them. Other plants like mandevilla vines have hairy leaves to help reduce excessive sun and heat from affecting plant tissues.
3) Salts – Sea water contains many dissolved minerals that remain in the soil after seaside plants and crops die or are harvested.
If these salts remain in the soil, the next crop may not be able to take root. This may not be a problem for some plants like succulents, but most crops cannot tolerate these high concentrations of salts.
Sea minerals may be beneficial for soil nutrients, but in high enough concentrations they can create an excessively alkaline soil environment. Most crops do not grow well in such conditions. Alkaline soils have a pH level greater than 7.0.
Sources & references used in this article:
The British seaside: Holidays and resorts in the twentieth century by JK Walton – 2000 – books.google.com
Greater perfections: The practice of garden theory by JD Hunt – 2000 – books.google.com
Seaside plants by WH Duncan, MB Duncan – Ecological Restoration, 1987 – er.uwpress.org
Associations of garden birds with gradients in garden habitat and local habitat by DE Chamberlain, AR Cannon, MP Toms – Ecography, 2004 – Wiley Online Library
Designing the seaside: Architecture, society and nature by F Gray – 2006 – books.google.com
Local and landscape drivers of predation services in urban gardens by SM Philpott, P Bichier – Ecological Applications, 2017 – Wiley Online Library
Local and landscape correlates of spider activity density and species richness in urban gardens by MD Otoshi, P Bichier, SM Philpott – Environmental entomology, 2015 – academic.oup.com