Signs of a Low pH in Plants

A soil pH number tells gardeners a range that helps them determine whether their soil is acidic, neutral or alkaline. Soils with a pH of 7 are neutral; below a pH of 7, acidic; and above a pH of 7, alkaline. A soil test can determine the type of soil and whether it is extreme in either direction, as these extremes in pH can make plants receive too many or not enough of valuable nutrients. Soil pH affects a plant's ability to grow. Plants with a low pH exhibit various symptoms.

Signs of Low pH

Low pH symptoms may vary among plants. However, soils with low pH may cause a release of aluminum that can stunt a plant's growth and alter nutrient intake. Some plants may also suffer with manganese and iron toxicity that causes yellow spots and leads to browning and leaf death. Other symptoms you may notice include wilting leaves, stunted growth, blighted leaf tips, yellowing of foliage or other leaf discoloration and poor stem development.

Why pH Matters

Acidic soils have a low pH, and this affects the plant's ability to absorb essential nutrients from the soil. Normal ranges for soil pH are between 5.0 and 8.5. It is when the levels go above or below these numbers that problems occur. For example, at pH values lower than 5.0, manganese and aluminum can become toxic to plants growing in that soil. Plants can get overloaded with these liberated nutrients and cannot process the excess quickly enough, leading to plant death.

Causes of Low pH

Several factors can affect a soil's pH level, causing it to drop. One such factor is rainfall that is naturally acidic because of the presence of carbonic acid, which results from the atmosphere's carbon dioxide and moisture. Environmental factors, such as where the rain falls, also has an effect on pH. It tends to be lower in cities, because the atmosphere near cities has more sulfuric and nitric acid from burning fossil fuels. The use of nitrogen fertilizers that contain ammonia also lowers a soil's pH level, and so does decomposing organic matter, which produces carbonic acid.

Adjusting Low Soil pH

A soil test can help you determine what your soil pH is. It is also important to know the soil texture, as the type of soil helps determine the amount of limestone needed. For example, clay soil requires more limestone than sandy soil. To raise pH, use dolomitic limestone, a combination of magnesium and calcium carbonate, which neutralize more acid and add magnesium to the soil. You can also use oyster shells or wood ashes to raise pH.

About the Author

Molly Allman


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