Natural Weed Killer
The use of common salt (either table salt, rock salt or water softener salt) represents a viable approach to killing lawn and garden weeds without introducing poisonous commercial chemicals into the soil. It is not always a foolproof method, however, and must be used with care to prevent damage to other desirable plants in the vicinity.
How Salt Kills Weeds
Nearly any soluble chemical will act as a weed killer. Some mixtures act as a poison, while others, like salt, kill plants by drawing the water from the foliage or by holding the moisture in the soil so that it cannot be absorbed by the roots.
Many recipes for home-brewed herbicides include sodium chloride. As a natural desiccant, salt--used either as a spray on tender foliage or as crystals applied to the soil near the weed--dehydrates the taproot of the plant in a chemical process called reverse osmosis.
Salt is most effective as a weed killer when a few granules are deposited on the soil near the base of the plant. As the salt leaches into the soil, the drying effect overcomes the roots and kills the plant.
Unlike commercial herbicides, salt is a non-selective killer and will just as effectively kill desirable plants if applied too heavily. The application must be accurately placed and of limited quantity to be effective. Many people use salt solutions to eliminate the grass and weeds that grow in the spaces between bricks or concrete slabs in walkways, patios or driveways. If salt is used in this manner, there is no danger of salt damaging neighboring plants.