Nearly every homeowner is aware of the importance of applying lime to the home lawn. However, few probably have a complete understanding of why liming can be an important aspect of the home lawn care program, how to determine if liming is needed and how one should go about applying lime to the lawn.

Why Do Home Lawns Need Lime?

Lime is applied to the soil of home lawns to increase the soil pH. Soil pH, a measure of the soil's acidity or alkalinity, can directly influence the vigor and quality of the home lawn. When the pH is below 7.0, the soil is said to be acidic; when above 7.0, it is alkaline.

Several factors cause the formation of acidic soil conditions. One primary cause is the leaching of base nutrients such as calcium, magnesium, and potassium from the soil. This occurs more frequently in areas of heavy rainfall or on heavily-irrigated turf. A second cause is the use of acidifying nitrogen fertilizers. Most of the fertilizers applied to lawns have the potential to cause acidic conditions. However, the extent to which fertilizer application will affect soil pH is dependent on a number of factors, including: type of nitrogen applied, amount applied, types of other nutrients present in the fertilizer, soil type and irrigation frequency. Other factors which may act to reduce soil pH are decomposition of soil organic matter and irrigation with acidic water.

When the soil pH drops below 6.0, a number of nutrients necessary for proper growth become less available for use by the turfgrass plant. These include: nitrogen, phosphorus, potassium, sulfur, calcium, magnesium and molybdenum. As these nutrients become less available, the lawn's color, vigor and ability to resist (or recover from) heat, drought or traffic stress will be reduced. Applications of enough lime to raise the soil pH above 6.0 can increase the availability of these nutrients, thus making it easier to maintain the quality and vigor of the lawn.

An excessively high (alkaline) soil pH (greater than 8.0) is just as undesirable as a low pH. When the pH exceeds 8.0, such nutrients as nitrogen, phosphorus, iron, manganese, boron, copper and zinc become less available for use by the turfgrass plants in the lawn. The result may be a less vigorous, unhealthy lawn. Over-application of liming products may cause the development of alkaline soil conditions.

Is Liming Necessary?

Most soil in Rhode Island is acidic and will benefit from lime. However, the only way to determine how much lime to apply is through the results of a soil test conducted at a state or commercial soil testing laboratory. A soil test kit or pH probe used by the homeowner, or at the local garden center, to test soil pH may indicate the need for liming. However, these simple tests do not allow one to determine how much lime is needed to correct the acidic condition. Individual soils can differ greatly in the amount of lime required to raise the pH to a specified level between 6.0 and 7.0. This amount of lime for a particular soil is designated as the lime requirement on soil test reports. See GreenShare Factsheet on soil testing for more information on how to obtain a soil test.

How Much Lime Should Be Applied?

Most soil test reports will indicate the lime requirement in pounds of pure calcium carbonate per acre, or per 1000 square feet. Since most liming products are not likely to be pure calcium carbonate, you will need to calculate how much product to apply to the lawn. To do this, find the number on the bag label which is called the CALCIUM CARBONATE EQUIVALENT - it will be stated as a percentage. Next, find the liming requirement stated in the soil test report. Using these two numbers, perform the following calculation:

Liming Requirement (from soil test) Calcium Carbonate Equivalent = Amount Of Product/Acre or /1000 Square Feet

If this amount exceeds the values in the table below, the amount recommended for your lawn should be divided in half and applied at two different times during the year.

When Is The Best Time To Apply Lime?

Lime can be applied at any time during the year. However, it should not be applied to turf that is wilted or frost-covered. The turf should be irrigated after application in order to wash any lime off of the turfgrass leaves.

Are All Liming Materials The Same?

As indicated in the table below, all liming materials are not the same. They can differ in price, safety, ease of application, calcium carbonate equivalent and rate at which they work. Note that gypsum (calcium sulfate) is not included in this table. Gypsum will change soil pH very little, if at all, and should never be considered as a liming material.

Liming Materials And Their Characteristics

*These are approximate values and will vary with the purity of the individual product.
**Maximum rate in pounds of product/1000 square feet. Multiply by 44 for rate in pounds/acre.

Adapted from John R. Street and Susan K. White, Ohio State University Extension, 2000