Liming a lawn involves applying ground limestone to the soil to maintain a healthy turf environment. The primary function of this soil amendment is to raise the soil’s pH level. By reducing acidity, lime creates a more favorable chemical environment for grass roots to thrive.
Lime is not a fertilizer, although it contains nutrients like calcium and sometimes magnesium. Its benefit is indirect; it corrects the soil chemistry so that nutrients already present or those added through fertilization can be utilized by the grass. Without this adjustment, a well-fertilized lawn may struggle to grow vigorously.
Diagnosing Soil Acidity
Before applying any lime product, it is necessary to determine the current pH of the soil, as guessing can lead to over-liming. Soil pH measures acidity or alkalinity on a scale from 0 to 14, where 7.0 is neutral and values below 7.0 are acidic. Most common turfgrasses perform best in a slightly acidic to neutral range, typically between 6.0 and 7.0.
A professional soil test, often available through a local cooperative extension service, provides the most accurate data, including the current pH and the amount of lime needed. While home kits offer a general estimate, they often lack the precision required for determining exact application rates. The test results are important because the soil pH scale is logarithmic; a reading of 5.0 is ten times more acidic than a reading of 6.0.
When the soil falls below the optimal 6.0 range, the grass struggles because essential nutrients become chemically bound and unavailable for absorption. Low pH can lock up macronutrients like nitrogen, phosphorus, and potassium, preventing the grass from taking them up through its roots. This condition results in a yellowing, stunted lawn that poorly responds to fertilization, making nutrients inaccessible.
Choosing the Right Lime Product
The best type of lime for a lawn depends on the soil test results, particularly the levels of magnesium. The two main types of limestone used as soil amendments are differentiated by their mineral composition. Calcitic lime is composed primarily of calcium carbonate and is the appropriate choice when the soil test indicates a low pH but adequate magnesium levels.
Dolomitic lime contains both calcium carbonate and magnesium carbonate. This product is recommended when the soil test reveals a deficiency in magnesium in addition to a low pH. Applying dolomitic lime when magnesium levels are already sufficient can lead to an imbalance.
Lime products are also available in different physical forms, with pelletized and pulverized being the most common. Pelletized lime is finely ground limestone compacted into small, uniform granules. This form is recommended for homeowners because it is easy to handle, flows smoothly through a standard fertilizer spreader, and produces very little dust.
Pulverized, or powdered, lime is the purest form of ground limestone and typically acts faster due to its fine particle size. However, it is difficult to apply evenly with home spreaders, creates a hazardous dust cloud, and can wash off the turf before settling. The pelletized form of either calcitic or dolomitic lime is the most practical and efficient choice for lawn care.
Proper Application Techniques
The timing and method of application are important for successful liming, as the material works slowly to change soil chemistry. The ideal time to apply lime is in the fall or early spring, as cooler weather and increased rainfall help move the material into the soil profile. Fall application is often preferred because the winter freeze-thaw cycles assist in breaking down the limestone.
The application rate must be based on the soil test recommendations, which account for the current pH and the soil type. Applying lime at the correct rate avoids over-liming, which can result in an excessively high pH that also locks up nutrients, causing issues like iron deficiency. If the recommended amount exceeds 50 pounds per 1,000 square feet, the application should be split into two separate treatments, spaced at least six months apart, to prevent turf damage.
Lime should be spread evenly across the lawn using a drop or broadcast spreader. To ensure uniform coverage, apply half the recommended amount walking in one direction and the remaining half walking perpendicular to the first pass. Immediately after application, the lawn should be watered to rinse lime particles off the grass blades and move the material down to the soil level where the chemical reaction takes place.