Lime is a soil amendment consisting of ground limestone rock. This material primarily contains calcium carbonate, and often includes magnesium carbonate. Its purpose is not to fertilize the grass directly, but rather to change the chemical environment of the soil. By altering the soil’s chemistry, lime supports a healthier growing medium for the turfgrass.
Modifying Soil Acidity
Lime’s main function is to neutralize soil acidity by raising the soil’s pH level. Soil pH measures the concentration of hydrogen ions, where a lower number indicates higher acidity. When lime dissolves in the soil, the carbonate components react with the acidic hydrogen and aluminum ions.
This reaction introduces basic ions, such as calcium and magnesium, which replace the acidic ions on the soil particles. This increases the soil’s pH value, moving it closer to a neutral or slightly acidic state. Because lime dissolves slowly, this shift in soil acidity is a gradual process that can take several months.
How pH Affects Grass Health
Raising the soil pH optimizes nutrient availability for the grass. When soil becomes too acidic (typically below a pH of 6.0), essential macronutrients like nitrogen, phosphorus, and potassium can become chemically locked up. If nutrients are locked up, the grass roots cannot absorb them efficiently.
Adjusting the soil to a less acidic range unlocks these nutrients, making them soluble and accessible for uptake. This improved nutrient environment supports robust root development and helps the grass maintain a vibrant green color. A balanced pH also enhances the activity of beneficial soil microorganisms that break down organic matter and cycle nutrients.
Identifying the Need for Application
The need for lime must be determined by a soil test. A professional soil test provides an accurate reading of the current pH level and offers specific recommendations for the amount of lime needed. Most turfgrasses thrive in a slightly acidic to neutral pH range, typically between 6.0 and 7.2.
Certain visual cues, such as a noticeable increase in moss growth, can suggest a low pH. Moss prefers acidic conditions and can outcompete turfgrass when the soil pH is too low. However, these visual indicators should only prompt a soil test, which is the only way to diagnose the specific imbalance and necessary application rate.
Potential Issues from Excessive Use
Applying too much lime can push the soil into an overly alkaline state. Over-liming can be just as detrimental as having soil that is too acidic. Excessively alkaline soil disrupts the nutrient uptake process, leading to a “nutrient lockout.”
In highly alkaline conditions, certain micronutrients, particularly iron and manganese, become insoluble and unavailable to the grass. This can result in iron chlorosis, a condition where the grass leaves turn yellow while the veins remain green. Over-liming counters the desired benefit of the application, causing the lawn’s health to decline.