Muriatic acid is one of the names for the chemical compound hydrochloric acid. It is often used as an industrial solvent, masonry stripper and an ingredient in several types of household cleaners. Concentrations of the acid, represented as a percentage mixed in water, vary among products. In all cases, hydrochloric acid has an extremely low pH and is highly caustic. It is not suitable for use as a soil acidifier. There are many safer alternatives.
Generally, hydrochloric acid is manufactured either by reacting hydrogen and chlorine gases in a controlled environment, resulting in non-aqueous hydrogen chloride, or as a byproduct of other chemical processes. When diluted in water, it is called hydrochloric acid or muriatic acid. Hydrochloric acid occurs naturally in the digestive tracts of humans and animals. It can cause serious irritation and chemical burns to exposed skin, eyes and mucous membranes, including the respiratory tract if it is inhaled as a vapor. It is also regulated as an environmental toxin by the U.S. Environmental Protection Agency. Store hydrochloric acid products in safe locations out of the reach of children or pets.
Soils and Testing
Usually, weathered soils that receive plentiful rainfall tend to be acidic. These often contain a high percentage of clay particles that lower the pH. Alkaline soils tend to be more common in drier climates and where limestone is a significant soil component. Before treating your soil to lower its pH, conduct a thorough soil test that assesses pH, chemistry and organic matter content. Select one from a local home and garden center or consult a landscape or extension service in your area.
Most sources recommend using elemental sulfur or sulfate fertilizers to lower soil pH to a desired range. Elemental sulfur, in powdered form, can be incorporated into soils or added as a top dressing to moist soils. Ammonium sulfate, aluminum sulfate and potassium sulfate are all granular compounds that can be applied as top-dressings and watered in or directly incorporated into soils. Use these according to label directions or on the advice of a certified horticulturalist. Where soils are naturally alkaline, repeated applications may be necessary at regular intervals.
Maintaining Soil pH
Very broadly, most plants grow best in soils that are slightly acidic and contain lots of organic matter. Heavy clays may be too acidic. Porous, sandy or limestone soils may be too alkaline. You can better maintain a consistent, desired pH by incorporating organic amendments where soils are deficient in these. Choices for this include finished composts and animal manures, green manures, leaf mold, peat moss and commercial soil conditioners. Avoid adding sand to clay soils and vice-versa. This can easily turn your lawn or garden into a brickyard. Also, peat moss works best for sandy soils. When mixed with other types of soil, peat moss can impede drainage and create boggy conditions. Pregnant or nursing women should wear gardening gloves when working in the soil for protection against soil-borne pathogens.