Liming a lawn is a way to raise the pH of the soil. Soil pH is measured on a scale of 0-14 with 7 being neutral. A soil pH below 7 is considered acidic while a soil pH above 7 is considered basic (alkaline). Bluegrass prefers soil pH 6-7. The pH of a soil is important because it affects the availability of different nutrients. Nitrogen, for instance, is more available at a soil pH of 6 than a soil pH of 5. Liming a soil with a pH of 5 would increase the amount of nitrogen available to the grass roots.
The best way to determine your lawn’s pH is to have the soil tested by your local Cooperative Extension Service. They will also be able to tell you how much lime or elemental sulfur to apply to reach the optimal level of soil pH. Many southern soils are acidic and will need approximately 50 pounds of lime per 1000 square feet. Whenever possible, purchase lime in pelletized form since it is much easier to distribute. Lime may take up to three months to affect the pH of your soil and can be applied at any time of the year.
Occasionally, you may encounter a Southern soil with a pH above 7.5. In these cases, Kentucky Bluegrass may develop iron chlorosis. This appears as a yellowing between the veins of a grass blade. In such a case, you can correct the problem by lowering the soil pH to the 6-7 range with an elemental sulfur product.