When Do I Add Lime to My Soil?
The ideal soil pH is slightly acidic, between 6.0 and 7.0. When the soil pH drops below 6.0 (becomes more acidic), certain nutrients needed for proper grass growth, such as nitrogen, phosphorus, potassium, and calcium, become unavailable to certain nutrients for proper growth and other plants. Lime can be applied to the soil to help increase the soil pH above 6.0.
However, unless you have a soil test done by a professional soil lab, don't bother applying lime to your lawn. A soil test kit or pH probe available at your local garden center will tell you your soil's pH, but will not tell you how much lime is needed to correct the problem. The amount of lime needed to correct the soil pH is dependent on soil type (how much sand and/or clay is present in the soil). Results from a professional soil lab will tell you how much lime to apply to your soil as pounds of pure calcium carbonate.
Liming materials are not pure calcium carbonate, but will list the "calcium carbonate equivalent" on the bag label. Not all liming materials are the same and vary in amounts calcium carbonate equivalents, ease of application, and rate of pH change. Pelletized limestone is the easiest to apply and will change the pH of the soil quickly after application.
Limestone is most effective at changing the soil pH when it is mixed into the top 5 inches of soil prior to the lawn being planted. For established lawns, limestone should be applied in either the spring or fall, but never when the lawn is wilted or dormant. Aerate your lawn with a core aerator first before applying the lime. Water the lawn immediately after applying limestone to rinse it off the grass blades.