Many gardeners do not want chemicals near their kids or on edible plants, instead preferring to use nontoxic herbicides when possible. One natural weed-killing method involves sprinkling a weed with salt or spraying it with concentrated salt water. Salt kills weeds by dehydrating them and preventing them from absorbing nutrition. Unfortunately, it also kills flowers, grass, vegetables and even trees. It can also linger in the soil, causing problems in your garden for years.
One of the ways salt water kills is by drying out the plant, much like using salt to make beef jerky. When the concentrated salt water comes in contact with leaves or stems, it pulls all the water out through the surface. In the soil it dehydrates roots, leaving the plant unable to absorb water or nutrients. Salt will also be drawn into the plant as roots absorb water. Once inside the roots, the salt prevents the plant from sending water through the stem and leaves of the plant, dehydrating the entire plant.
Salt water does more than dehydrate. Once absorbed by a plant, salt interferes with the plant’s ability to produce chlorophyll and to photosynthesize. Since these are the main sources of energy for a plant, the plant slowly starves to death. Salt also replaces nutrients in the soil, so plants cannot absorb what they need to survive. Salt water is very effective at killing plants. It is just as effective at killing your vegetables, lawn and flowers, too.
No matter how carefully you spray concentrated salt water, it will affect neighboring plants as well. Once the salt is on the weed, the weed will die. When this happens the salt ends up in the soil, and all it takes is a little bit of water for the salt to seep into your soil and come into contact with the roots of other plants such as your flowers or lawn grass. So, the more salt water you use on weeds, the more potential damage to the rest of the yard.
The only way to remove salt from your soil requires a lot of water as salt dissolves in water. As the water goes deeper into the soil or down a drain, it takes a certain amount of salt with it. While this does eventually remove the salt from your garden, it puts the salt into the water table, which is not good for the environment. How long it takes to remove salt from the soil depends on the concentration.