Q. Have you ever heard of adding vinegar or citric acid when fertilizing plants in our area? A. Quite a few people have thought about it or tried it but the positive impact on the soil is short-lived and is usually considered not worth doing. Gardeners realize our soil is much more alkaline than the ideal garden soil. Methods used to acidify soils are frequent gardening topics. This includes the addition of acids such as acetic or vinegar and adding sulfur. Sulfur granules can sit on the surface of a desert soil for months or even years if it never comes in contact with water or is not ground finely. This does not help lower soil pH.             Our soils and our tap water from Lake Mead carry a lot of lime so the addition of anything to the soil to make it more acidic is usually short-lived.  A fairly effective long-term method for improving our soil is the addition of compost or other sources of organic matter that decompose, acidifying the soil as it does so.             However, adding weak acids to the soil is a short-term solution. How much acid to add to a soil is another question altogether. Much of that depends on the chemistry of the soil itself and varies from soil to soil.             Acidifying water used for foliar applications of a pesticide or fertilizer is a different story. This water should always be acidified to pH around 6.5 before adding the pesticide or fertilizer. The easiest way to measure this pH is with litmus paper, the type used for swimming pools or aquariums. Another option would be to use distilled or reverse osmosis water instead.