Perhaps one of the most misunderstood of all lawn care practices has to do with the application of lime. Most folks fall into three main categories of understanding when talking of “liming” their lawns. The first group has absolutely no idea what liming is and what it’s all about, and that’s okay. The only worries I have about this group of people is when their lawn care provider tells them it’s time for their “annual lime application”. Without even thinking about it, some homeowners end up spending money on something they think is just routine and normal lawn care, just because someone said they should. If not careful, this category of people can be taken advantage of. The next type of people fall in the category of what I call “traditionalists”. They apply lime to their lawns every year simply because it’s what they have always done. I once talked to a guy who admitted he didn’t really know exactly why he needed to add lime to his lawn every year; he just knew it had something to do with the soil. Granted, it does have something to do with the soil. The last category of people are well informed and understand perfectly well why, what, when, and how lime is applied to a lawn. These people are rare, so for the benefit of everyone I will give a brief overview on the subject lime, soil, and grass. 

What is Lime?

First, what is lime? Agricultural lime comes in many forms, but generally consists of a compound made up of calcium or calcium and magnesium. The most common form of this compound comes in a finely ground powder or pellet, and is made of ground limestone which is almost pure calcium carbonate. Burnt and hydrated lime are other types which act much faster than ground lime, but can also be hazardous to handle and are often more difficult to apply.  

The pH Scale

So why do we sometimes add these lime based compounds to our lawns? Contrary to popular belief, lime is not a fertilizer. Its main purpose is to amend the pH of a soil. If it’s been a while since you’ve taken chemistry, let me explain. pH is a measurement of how acidic or alkali a substance is, and rates substances on a scale from 0 to 14 . For example, vinegar, lemon juice, and soda are all common acids which are known as being acidic. On a pH scale, these substances would have a rating lower than 7. Substances with a pH rating greater than 7 are alkali, and are known as being base. Base substances include bleach, baking soda, and ammonia. 

Adding Lime Increases Soil pH

The soils in our lawns are no exception to this pH scale. Soil too can be either acidic or alkali, and plants such as grass prefer a certain range. Most grass species like the pH of a soil to be between 6.0 and 7.0 (slightly acidic). Sometimes the soil found in our yards can have a pH lower than 6, tipping it into the very acidic category. This is more common in the eastern portion of the United States than the West. When this happens, a number of nutrients necessary for proper lawn growth become less available for use. Grass color, vigor, heat tolerance, pest and disease resistance, and traffic tolerance all start to suffer as a result of an acidic soil. So, to increase pH back into the desirable range, lime is added. It’s the same concept as taking an antacid for heartburn. In fact, the same calcium carbonate that makes up the antacid tablets we take for heartburn is the same calcium carbonate that helps a soil recover from its acid problems. 

Get Your Soil Tested Professionally

So how do we know if the soil in our lawns needs this acid relief? The only sure way is by getting your soil tested by a state or commercial soil testing laboratory. Many times homeowners will buy soil test kits found at many garden centers. These do-it-yourself kits may tell you that your soil needs lime, but they don’t tell you how much. Over-applying lime is just as bad as having an acidic soil since this then pushes your soil into the alkali category which requires its own special solutions to correct. Professional soil tests on the other hand will not only let you know if liming is necessary, but will let you know how much lime you need to apply. These professional tests can be attained with help from your local Cooperative Extension service or private soil testing labs. 

When and How to Apply Lime

Once you have determined that your soil needs lime, the best time to apply it is just before planting grass seed. For established lawns, any time during the year will work as long as it’s not applied to a lawn that is too wet, wilted, or frost-covered. Be sure to spread it evenly over the entire area as lime will not spread horizontally in soil. When applying lime in the pelleted form, a spreader is the best way to achieve an even spread. To figure out how much lime to apply, always check the label on the lime product to find out how much calcium carbonate the product contains since most liming products are not pure calcium carbonate. After that, consult your soil test results to find out the exact liming requirement. And unless your soil test says otherwise, yearly applications of lime are strongly discouraged. 

Only Apply When Needed

You wouldn’t take an antacid if you didn’t have heartburn would you? Then why apply lime to a lawn that doesn’t need it? While liming does have its place in proper lawn maintenance, it should only be applied when needed to correct an acidic soil, and then only after a professional soil test. Most places in the United States are actually within the preferred pH range (or even slightly higher) and liming would be useless, or even damaging to a soil. So the next time someone tells you your lawn needs lime added, be sure to ask how they came to that conclusion.