What Causes Salt to Kill Plants?

by Robert Alley
Salt has been used as a weapon to destroy an enemy's crops.

Salt has been used as a weapon to destroy an enemy's crops.

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No one pours salt on their plants. They do pour salt on their driveway, walkway and steps in the winter to melt ice. At the same time highway crews apply salt to roadways to clear ice. Some of that salt ends up on plants, with adverse effects. The chemical makeup of salt damages and kills plants in several ways.

Sodium

Salt is a combination of sodium and chloride, or NaCl. Salt melts ice and then dissolves in the resulting water. The dissolved salt separates into sodium and chloride, both of which are toxic to plants. The water with sodium goes into the soil. The sodium replaces minerals that are essential to plant growth, such as calcium and potassium. The loss of these nutrients prevents plants from growing and can lead to their death.

Chloride

The chloride in dissolved water gravitates to the roots of plants, damaging them and preventing growth. From there the plant takes up the chloride and transports it to leaves. The chloride affects the leaves by interfering with photosynthesis, the process the plant uses to convert sunlight into the energy needed to keep it alive. Chlorophyll production is the casualty of the chloride in the leaves. Chlorophyll is the chemical substance in leaves that absorbs sunlight and converts carbon dioxide and water into carbohydrates for plant growth, with oxygen as the by-product.

Salt Spray

Plants that are close enough to roadways or driveways risk damage from salt spray. The salt lands on the leaves and has the effect of making the plant more vulnerable to cold damage. If possible, avoid locating plants where salt spray is likely. If that is not possible, then cover plants during times when salt usage is likely.

Osmosis

Plants rely on osmosis to absorb needed nutrients contained in water. Osmosis is a process of transferring water to maintain equal pressure. Salt inhibits this process, causing unequal osmotic pressure in plant cell membranes. This pressure collapses the cells, preventing the plant from growing. Salt also prevents flowering and seed germination, which contributes to the death of plants.

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