Vinegar can be used in the garden as an herbicide, a deterrent to cats and ants, a rust cleaner for garden tools and a freshener for cut flowers. Vinegar is sometimes touted as a fertilizer and pH balancing agent, but neither use is realistic.
As an herbicide, vinegar has limited use. The acetic acid in vinegar does burn the leaves and membranes of plant tissue, but it does not have any effect on the roots. It also has the same effect on desirable plants as it does weeds. This makes vinegar as an herbicide only moderately effective on small weeds during the dormant periods of other plants. It is also not useful as a fertilizer as its main ingredients are carbon, hydrogen and oxygen, which plants receive through the air. Large quantities of vinegar are required for it to be of use in balancing the pH of soil.
However, vinegar may be used as a deterrent for pests such as ants and cats. Sprinkle vinegar around the perimeter of the garden to keep these pests out. Freshly cut flowers from a garden benefit from two tablespoons of vinegar and one teaspoon of sugar in a quart of water. A mixture of half vinegar and half water can be sprayed on brick or limestone to eliminate calcium buildup.