Vinegar is a popular remedy for killing grass and weeds. The acetic acid in vinegar injures and kills cell membranes and dries up the leaves of a plant, causing the leaves to die. Spray undiluted vinegar on the grass and within a day day or two you will see it start to die. Household vinegar, which is a 5 percent acetic concentration, is not as successful as vinegar that has a 15 to 20 percent concentration. You can find this type of vinegar at hardware stores and some garden centers. A study published by the Oklahoma Agriculture Experiment Station in 2005, showed that a 20 percent solution is very effective for killing grass. A 2002 study done for the USDA found a 20 percent acetic acid level killed weeds and grasses with a 95 to 100 percent success rate. (Care must be taken when working with a higher concentrate because it can burn your skin.) Vinegar with a 5 percent acetic acid will not kill the roots of a plant on the first application. This means perennial plants, like many grasses, will most likely reappear. Therefore, repeated applications of vinegar, with a small amount of liquid dish soap to help the acid adhere to the grass, will be necessary to completely kill grass. Spraying a stronger vinegar shortly after mowing on a hot day will successfully kill perennial grasses.
Black Plastic or Newspaper
Plants need sunlight to survive---without it they die. If you cover the area of grass with black plastic, the grass underneath will eventually die. It may take several weeks, but because not only is the grass cut off from sunlight but also moisture and subjected to the heat trapped by the black plastic, the total plant---roots and all---will die without harming the soil. Multiple layers of newspaper (black-and-white pages only) can be used in much the same way, and the newspaper will eventually biodegrade.
For Small Areas & Cracks
One of the most bothersome places unwanted grass grows is in between bricks, stones and sidewalk cracks. A fast and easy way to permanently kill the grass in these areas is to pour boiling water on the grass. It will kill the entire plant quickly. Another method is to pour table salt on the plant and in the cracks. This, too, will kill the grass but also affect the soil so that no plant can grow. This works well for driveways and sidewalks but not in areas you may wish to grow something later.