Lime is a common soil amendment in lawn care, typically consisting of finely ground limestone rock, which is chemically either calcium carbonate or dolomite (a blend of calcium and magnesium carbonate). Lime is applied to modify the soil’s chemical properties, creating a more favorable environment for turfgrass growth. While lime offers significant benefits to a struggling lawn, its application requires precision. Applying an excessive amount can shift the soil chemistry too far, leading to detrimental problems that negatively impact the health and appearance of the grass.
The Purpose of Liming
The primary function of applying lime is to increase the soil’s pH, effectively reducing its acidity. Most common turfgrass species thrive in a slightly acidic to neutral range, typically between 6.0 and 7.0. When soil becomes too acidic, certain chemical reactions occur that bind up essential nutrients, making them unavailable for the grass roots to absorb.
By raising the pH into the ideal range, lime unlocks the availability of major plant nutrients like nitrogen, phosphorus, and potassium. This improved nutrient cycling allows the grass to efficiently absorb the fertilizer and organic matter already present in the soil. The result is a healthier, more vigorous lawn that exhibits better color and density. This process should always begin with a professional soil test, which provides a precise current pH reading and a specific recommendation for the exact amount of lime needed to achieve the target level.
How Excessive Lime Damages Grass
When lime is over-applied, it pushes the soil pH beyond the neutral point of 7.0, causing the soil to become too alkaline, often reaching levels of 7.5 or higher. This high alkalinity triggers a phenomenon known as mineral antagonism, which is the direct mechanism of damage to the turf. The high concentration of calcium from the lime chemically reacts with necessary micronutrients, rendering them insoluble.
This induced deficiency targets micronutrients such as Iron (Fe), Manganese (Mn), and Zinc (Zn), which are necessary for plant processes like photosynthesis. Although these elements may still exist in the soil, the elevated pH locks them into chemical forms that the grass roots cannot take up. This micronutrient lock-up leads to the visual symptom of chlorosis, which is a pronounced yellowing of the grass blades.
Iron deficiency is the most common result, causing the newest growth to turn pale yellow while the older leaves retain their green color. This pattern occurs because iron is immobile within the plant and cannot be relocated from old tissue to new growth. An over-limed lawn will display this characteristic yellowing and may also exhibit stunted growth due to the shortage of these micronutrients.
Fixing an Over-Limed Lawn
Correcting a lawn that has been over-limed requires patience and a systematic approach to gradually lower the soil pH. The first step involves increasing the amount of water applied to the lawn. Heavy and consistent watering, without causing runoff, can help move some of the soluble lime compounds away from the root zone over time.
For a more direct solution, homeowners must apply an acidifying soil amendment, primarily elemental sulfur. Microorganisms in the soil convert the elemental sulfur into sulfuric acid, which then neutralizes the excess alkalinity and lowers the pH. Application rates for elemental sulfur must be determined by a second soil test, but generally range from 1 to 5 pounds per 1,000 square feet, depending on the severity of the alkalinity.
It is crucial to apply the sulfur in small, controlled doses rather than a single heavy application to avoid further damage from over-correction. Because the conversion of sulfur into acid is a biological process, it works most effectively when soil temperatures are warm. Multiple gradual applications may be necessary to restore the soil to a healthy range.