Lime is a common soil amendment used to correct soil acidity, resulting in a greener, healthier lawn. When applied correctly, lime optimizes the environment where turfgrass thrives. Determining the precise amount needed is crucial, as applying too much or too little can be counterproductive. This article guides homeowners on understanding why and how much lime to use for effective results.
Understanding Soil pH and the Need for Liming
Soil acidity and alkalinity are measured on the pH scale, which ranges from 0 to 14, with 7.0 being neutral. Values below 7.0 indicate acidic soil, and values above 7.0 indicate alkaline soil. Most turfgrass varieties prefer a slightly acidic to neutral range, typically between 6.0 and 7.0, for maximum health and nutrient uptake.
When soil becomes too acidic (below 6.0), essential nutrients become unavailable to the grass roots. This low pH prevents the grass from absorbing nutrients like Nitrogen, Phosphorus, and Potassium, even if they are present in the soil. This lack of nutrient access leads to stunted growth, yellowing, and a weak lawn susceptible to weeds and moss. Lime, derived from ground limestone, neutralizes the acidity by introducing calcium carbonate or magnesium carbonate, raising the pH to the ideal range.
Determining the Correct Application Rate
The amount of lime required is unique to every lawn and must be based on a recent soil test. Soil testing determines the current pH and the soil’s buffering capacity, which is its ability to resist a change in pH. The test results, often provided by a local university extension office or commercial lab, recommend a specific lime application rate in pounds per 1,000 square feet.
The recommended rate depends on several factors, including the target pH for your specific grass type and the soil texture. Clay soils have a higher buffering capacity due to their finer particles, meaning they require a significantly larger amount of lime to achieve the desired pH change compared to sandy soils. For instance, a sandy soil might require two tons of lime per acre for a pH shift, while heavy clay soil might need four to six tons per acre.
The type of lime also influences the rate, as the recommendation is based on a material with a specific neutralizing value. Calcitic lime (calcium carbonate) is generally preferred unless the soil test indicates a magnesium deficiency. If magnesium is needed, dolomitic lime (magnesium carbonate) should be used. To avoid shocking the soil or causing nutrient imbalances, apply no more than 50 pounds of lime per 1,000 square feet in a single application. If the required rate is higher, split the application into two separate treatments, often six months apart.
Practical Guide to Spreading and Timing
The best time to apply lime is generally in the fall or early spring, allowing ample time for the material to break down and affect the soil pH. Fall application is advantageous because winter’s freeze-thaw cycles and moisture help incorporate the lime particles deeper into the soil. Avoid applying lime in the summer, especially during periods of drought or extreme heat, as it can stress the lawn.
Lime should be applied using either a broadcast (rotary) spreader or a drop spreader to ensure uniform distribution. Achieving even coverage is important, so the most effective technique involves splitting the total recommended amount in half. Apply the first half by walking back and forth across the lawn in one direction (e.g., north to south). Then, apply the second half by walking perpendicular to the first pass (e.g., east to west), creating a crisscross pattern. After application, lightly water the lawn to wash the lime off the grass blades and help it settle into the soil, beginning neutralization.