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Why Does Salt Work As a Weed Killer?

Updated April 17, 2017

Salt works as a weed killer primarily because it is a desiccant. Salt absorbs moisture from any nearby source. When dry salt is sprinkled on plant leaves, a process called 'exosmosis' occurs: the water content of the leaf is drawn out of the leaf and into the salt. This results in dead brown spots on the leaves with a "burnt" appearance. Enough salt on the leaves will dry out the plant to the extent that it ceases its life functions.

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Salt Dessicates Leaves

Salt works as a weed killer primarily because it is a desiccant. Salt absorbs moisture from any nearby source. When dry salt is sprinkled on plant leaves, a process called 'exosmosis' occurs: the water content of the leaf is drawn out of the leaf and into the salt. This results in dead brown spots on the leaves with a "burnt" appearance. Enough salt on the leaves will dry out the plant to the extent that it ceases its life functions.

Salt Is Soaked Up Through Plant Roots

Plant roots soak up salt water solution the same way they absorb other water. This distributes salt into every cell within the plant, which interferes with the plant's functions and dehydrates it from within, much in the same way that drinking salt water makes a person more thirsty. Plant species vary in their tolerance for salt content in the water they absorb. Plants growing near the ocean tend to have high salt tolerance. Plants that tolerate road salt will out-compete other species along northern roadsides. All plants will die if regularly fed a salt water solution at higher concentrations than they can naturally tolerate. This fact can be used to the advantage of a gardener wishing to kill a particular plant, such as a dandelion or invasive species, by applying salt solution as a weed killer.

Salt Lowers Resistance to Disease

High salt concentrations within a plant lead to molecular damage and disrupt plant growth. While this may not kill the plant outright, it makes the plant significantly more susceptible to insect damage and disease. Salt weakens a plant, either killing it or diminishing its condition so that other forces will do so. Together with external dessication and internal dehydration, its weakening impact on plants makes salt an effective weed killer.

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About the Author

A freelance writer since 1978 and attorney since 1981, Cindy Hill has won awards for articles on organic agriculture and wild foods, and has published widely in the areas of law, public policy, local foods and gardening. She holds a B.A. in political science from State University of New York and a Master of Environmental Law and a J.D. from Vermont Law School.

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