The health of turfgrass is connected to the soil’s chemical environment, specifically its acidity or alkalinity (pH). pH measures hydrogen ion activity on a scale from 0 (acidic) to 14 (alkaline), with 7 being neutral. Maintaining the soil pH within a preferred range is a fundamental consideration for successful lawn care.
Understanding Soil pH and Grass Needs
Most common turfgrass species, including Kentucky Bluegrass, Fescue, and Ryegrass, thrive in a slightly acidic to neutral pH range (6.0 to 7.0). This slightly acidic environment maximizes the availability of the major nutrients grass requires for growth. When the pH drops below this ideal range, the chemical balance of the soil negatively affects the grass.
Highly acidic conditions (below pH 5.5) severely limit the availability of essential nutrients like phosphorus, nitrogen, and potassium, locking them away from the root systems. Low pH also increases the solubility of elements such as aluminum and manganese, potentially raising them to toxic levels that inhibit root development. If the pH is too low, the grass cannot properly absorb nutrients, even with regular fertilizer application.
Signs of Excessive Soil Acidity
A lawn struggling with low pH often exhibits several visible symptoms. One noticeable sign is the yellowing of grass blades, known as chlorosis, which suggests deficiencies in nutrients like iron or magnesium that become less available in acidic soil. The grass may also display stunted or poor growth, appearing patchy or thin, because the roots are unable to take up nutrients.
The presence of certain weeds and indicator plants also provides clues about low soil pH. Moss and clover, for example, thrive in highly acidic conditions where turfgrass struggles and weakens. If regular fertilization does not produce vibrant, green growth, it indicates that the soil’s acidity is interfering with nutrient uptake.
Measuring Soil pH
Determining the pH level is the first step toward correcting an acidic lawn. Homeowners can purchase simple testing kits or digital meters from garden centers, which offer a quick, though less precise, reading of the soil’s acidity. These tests serve as a useful spot-check but may not provide the comprehensive detail needed for accurate long-term treatment.
A more reliable method involves sending soil samples to a professional laboratory, often through a local cooperative extension office. The laboratory analysis provides a precise pH reading and typically includes recommendations for the necessary amount of amendment. When collecting samples, take cores from several different areas across the lawn and mix them to get a representative average of the soil composition.
Adjusting Overly Acidic Soil
The primary method for raising the pH of overly acidic soil is the application of agricultural lime, a natural product made from pulverized limestone rock. Lime works by introducing calcium carbonate or magnesium carbonate, which neutralizes the hydrogen ions responsible for acidity. Soil test results are crucial because they dictate the exact amount of lime required; applying too much at once can shock the grass.
There are two main types of lime: calcitic lime (primarily calcium carbonate) and dolomitic lime (containing magnesium carbonate in addition to calcium). If the soil test reveals a magnesium deficiency, dolomitic lime is the preferred choice to raise the pH while supplying this micronutrient. If magnesium levels are sufficient, calcitic lime is used to avoid an imbalance, and it often reacts faster in the soil than dolomitic lime.
Lime is best applied using a broadcast spreader, ensuring even distribution across the lawn surface. The optimal time for application is usually fall or early spring, allowing the material several months to dissolve and alter the pH before the summer growing season. Since lime is slow-acting, it may take several months for the full effect to be seen, and a retest should confirm the pH has reached the target range. For highly acidic soils, split applications over multiple seasons are often recommended to prevent rapid pH swings.