Why Add Lime?

When it comes to your lawn, the ideal soil pH level is slightly acidic, between 5.8 and 7.0. Cool-season grasses (Kentucky bluegrass, ryegrass, and fescues) prefer a slightly higher, or more alkaline, pH. Warm-season grasses, on the other hand, prefer a slightly lower, or more acidic, pH. When the soil pH becomes too acidic, though, certain nutrients needed for proper growth (such as nitrogen, phosphorus, potassium, and calcium) become unavailable to the lawn, so the grass is unable to grow properly. Lime (sometimes called garden lime) or limestone can be applied to the soil to help increase the soil pH and make those nutrients more available.

Test Before Adding Lime

Before you add any lime into your yard, make sure that you submit a soil sample to your local county extension service for testing. The soil report you will receive from them will tell you how much lime needs to be added to your soil—something an at-home soil pH test from your local garden center can't do. The amount of lime needed to correct the soil pH will depend on your soil type (how much sand and/or clay is present in the soil).

When to Add Lime to a Lawn

Lime can take several months after application to break down and change your soil pH. A good time to test your lawn's pH and adjust it (if needed) is when your soil begins to warm in the spring. Lime can also be applied in the fall. The benefit of adding lime to your soil in fall is that both the freeze-thaw cycles and the abundant rain and snow common during the fall and winter months will help break down the lime and start raising the soil's pH. Lime should never be applied to a lawn that is stressed or dormant.

What Type of Lime to Buy

Limestone can be derived from either calcitic lime or dolomitic lime. Calcitic lime is the preferred type, thanks to the added plant benefits provided by the calcium. There are several types of calcitic lime products available, including agricultural ground limestone, pulverized limestone, and pelletized limestone. While both pulverized and pelletized limestone will change the pH of the soil relatively quickly, pelletized limestone is the easiest to apply. (Pulverized limestone is very dusty.)

While the results of your soil test will tell you how many pounds of pure calcium carbonate to apply to your soil to raise the pH, liming materials are not pure calcium carbonate. Look for the "calcium carbonate equivalent" on the bag label, which will vary depending on the liming material.

How to Apply Lime

Lime should only be applied to a dry lawn, and never to a lawn that is dormant, wilted, or stressed. Limestone is most effective at changing the soil pH when it is mixed in with the top 5 inches of soil, which means it's easier to adjust your soil's pH before planting grass seed or laying sod than it is to add it to an established lawn. Once you've applied lime to correct your soil's pH, chances are you will not have to re-lime for several years.

Before adding lime to an established lawn, aerate the lawn with a core aerator to open up space for the lime to move into the soil. Next, using a drop or rotary spreader (never lay down lime by hand), apply the limestone to your lawn. Apply half while walking over your lawn in one direction, then apply the other half in a direction that is perpendicular to your first. This will ensure that every part of your lawn is covered with lime.

According to a University of Arkansas Cooperative Extension Service publication, if your soil test results call for less than 50 pounds of lime per 1,000 square feet, it can be applied in a single application, either in the spring or fall. If you need between 50 and 100 pounds of lime, apply half in the spring and half in the fall. If you need to add more than 100 pounds of lime, apply 50 pounds in the spring, 50 pounds in the fall, then retest the following spring and add more lime if needed until you reach the desired soil pH. Never add more than 50 pounds of lime per 1,000 square feet in a single application. After you've applied the lime, immediately water your lawn to rinse any extra lime off the grass blades to prevent leaf burn.

Maintaining Your Lawn's pH

Allow the lime to work for several months, then have your soil professionally tested again. For example, if you applied lime in the spring, test again in the fall. If your soil is still too acidic, you can apply additional lime based on the recommendations of the soil test. If your soil pH is where it should be, you will not need to do anything else. Going forward, check your soil every 1 to 2 years to see if it is becoming too acidic. Remember: Always test your soil before adding lime.

Resources:

Patton, Aaron. Liming Your Lawn. FSA6134. University of Arkansas Cooperative Extension Service.

https://www.uaex.edu/publications/PDF/FSA-6134.pdf