Agricultural lime is a common soil amendment made from pulverized limestone, primarily composed of calcium carbonate or a combination of calcium and magnesium carbonate (dolomitic lime). It is regularly used in turf management to adjust the soil’s chemical balance. Homeowners often question whether this widely used product poses a threat to turfgrass health. Understanding its intended function and potential misuse is the first step in ensuring a healthy lawn.
The Purpose of Lime in Lawn Care
The fundamental reason for applying lime is to raise the soil’s pH level, making it less acidic and more alkaline. Factors like rainfall, decomposing organic matter, and nitrogen fertilizers naturally cause soil to become acidic over time. Most turfgrass species thrive in a pH range between 6.0 and 7.0.
When soil pH drops too low (typically below 5.5), the acidic environment hinders the grass’s ability to thrive. Low pH restricts the availability of major nutrients, including nitrogen, phosphorus, and potassium, even if they are present. Lime restores this balance, allowing grass roots to properly absorb necessary elements for vigorous growth and promoting beneficial microbial activity.
When Lime Can Cause Acute Damage
Agricultural lime, when correctly applied, does not directly kill grass, but immediate damage can occur under specific conditions. Acute injury is most often seen when highly concentrated or caustic forms of lime are used instead of the standard agricultural product. For instance, using hydrated lime or quicklime is strongly discouraged because these forms are highly caustic and can chemically burn the grass blades and roots.
Acute damage also happens when standard agricultural lime is applied incorrectly, particularly in massive, localized clumps. A thick pile of lime sitting directly on the grass can smother the turf, preventing gas exchange and sunlight access. The high concentration of material can also chemically burn the grass and roots in that small area, leading to visible, dead patches.
Recognizing Symptoms of Over-Liming
The more common consequence of misapplying lime is over-liming, which raises the soil pH to an excessively alkaline level, typically above 7.5. This high alkalinity causes nutrient lockout, where many essential micronutrients become chemically unavailable to the grass roots.
This restriction visibly impacts the uptake of micronutrients like iron, manganese, and zinc. The resulting deficiency manifests as chlorosis, a distinctive yellowing of the grass blades. Since iron is necessary for chlorophyll production, its deficiency causes the grass to look pale or yellow, particularly on newer growth. This chronic damage is often mistaken for a nitrogen deficiency, but it is actually a problem of nutrient access caused by the high soil pH.
Essential Steps for Safe Application
The most crucial step before applying any lime is to conduct a professional soil test. Guessing the amount of lime needed is the primary reason for over-liming, which can severely damage a lawn. The soil test report provides the current pH level and a precise recommendation on the amount of liming material required per unit area.
Once the correct rate is determined, use a drop or broadcast spreader to ensure the pelletized lime is distributed uniformly across the turf. If the recommended amount exceeds 50 pounds per 1,000 square feet, the application should be split into two or more separate treatments spaced several months apart. Immediately after application, watering the lawn thoroughly helps wash granules off the grass blades and begins moving the lime into the soil.