Agricultural lime is a soil amendment derived from crushed, naturally occurring limestone rock. This material is primarily composed of calcium carbonate, though some varieties, known as dolomitic lime, also contain magnesium carbonate. The main purpose of applying this substance is not to fertilize the lawn, but to neutralize soil acidity by raising the pH level. This correction creates a healthier environment for turfgrass, allowing it to better access the nutrients it needs to thrive.
Why Soil Acidity Requires Correction
Soil acidity is measured on the pH scale, where a reading below 7.0 indicates acidic conditions. When soil becomes too acidic, typically below a pH of 6.0, it severely restricts the chemical availability of essential plant nutrients. This low pH environment effectively “locks up” macronutrients like phosphorus, nitrogen, and potassium, preventing grass roots from absorbing them even if they are physically present in the soil.
Furthermore, strongly acidic soil can cause elements like aluminum to become soluble, which can be toxic to turfgrass roots and inhibit growth. This nutritional imbalance leads to weak, pale, and sparse turf that is highly susceptible to stress, disease, and pests. Low pH also favors the growth of certain unwanted species, such as moss and acid-loving weeds, which outcompete the struggling grass.
Determining If You Need to Apply Lime
Applying lime without first knowing your current soil pH is a common error that can be wasteful or even harmful. Over-liming can push the soil into an alkaline state, which causes different nutrient deficiencies, particularly affecting the availability of iron and manganese. Therefore, the only reliable way to determine your lawn’s needs is through a proper soil test.
You can purchase do-it-yourself kits, which provide a general pH range using color-changing reagents or test strips. However, for a precise and actionable result, sending a soil sample to a professional laboratory, such as a local university extension office, is recommended. Professional tests provide the exact pH reading and specify the quantity of lime (measured in pounds per thousand square feet) required to reach the target range.
For most turfgrass species, the optimal soil pH range falls between 6.0 and 7.0, which is considered slightly acidic to neutral. Soil test results account for soil type; clay soils require significantly more lime to adjust the pH compared to sandy soils due to their higher buffering capacity. Once you have the specific recommendation, you know precisely how much material to apply.
Optimal Seasonal Timing for Application
Lime is a slow-acting amendment; it works gradually over several months rather than dissolving instantly. This slow reaction rate makes the timing of the application paramount for maximum effectiveness. The best time to put lime down on a lawn is typically in the late fall or early winter.
Applying lime in the cooler seasons allows the natural freeze-thaw cycles and abundant moisture from winter rain and snow to work the material into the soil profile. This process helps dissolve the lime particles and moves the neutralizing calcium deeper into the root zone before the next active growing season begins. By spring, the soil pH will have begun to rise, ensuring the grass can immediately access newly applied fertilizers.
A secondary application window exists in the early spring, but it is less ideal because it can temporarily interfere with the efficacy of pre-emergent herbicides, which are often applied around the same time. If you must apply lime in the spring, do so as early as possible to allow for maximum breakdown before temperatures rise. Always wait four to six weeks between applying lime and applying any fertilizer or herbicides to prevent chemical reactions that could reduce the effectiveness of either product.
Practical Steps for Applying Lime
Before spreading the lime, mow the grass to its normal height and ensure the soil surface is slightly moist; this helps the product stick and begin dissolving. You should choose a product that is pelletized or granulated, as these forms are less dusty than pulverized lime and flow more uniformly through a standard spreader. Calcitic lime is generally preferred for lawns, though dolomitic lime is suitable if a soil test specifically indicates a magnesium deficiency.
Use a drop or broadcast spreader to apply the material evenly at the rate prescribed by your soil test. To ensure uniform coverage and avoid streaking, apply half of the recommended amount by walking in one direction, such as north to south, and the remaining half in a perpendicular direction, such as east to west. Following the application, lightly water the lawn to wash the lime off the grass blades and start the process of moving it into the soil. Finally, sweep any granular material off sidewalks and driveways to prevent staining.