Many homeowners will apply lime to their lawn once a year with the hopes of improving the quality and density of the turfgrass. However, there may not be a complete understanding of why a lime application (i.e., liming) can be an important aspect of a home lawncare program, how to determine if liming is needed, and how one should go about effectively 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 pH is above 7.0, soil is alkaline; and pH of 7.0 is considered neutral. For turfgrasses used in Ohio home lawns, a soil pH between 6.0 and 7.0 (slightly acidic) is ideal. Many of our home lawn grass species prefer these types of pH ranges. Turf outside of these ranges can lose quality.
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 lawns. A second cause is the use of acidifying nitrogen fertilizers. Most of the fertilizers applied to lawns have the potential to cause acidic conditions over time. However, the extent to which fertilizer application will affect soil pH is dependent on a number of factors:
- type of nitrogen applied
- amount of nitrogen applied
- types of other nutrients present in the fertilizer
- soil type
- irrigation frequency
Fertility products that have a sulfur element added to them will potentially have the greatest impact on causing acidic soil conditions. Other factors that may act to reduce soil pH are decomposition of soil organic matter and irrigation of soil with acidic water. The surrounding landscape may also have an impact. For example, pine tree needles have the ability to acidify the soil over time, and lawn areas near those trees should be monitored for soil pH. Based on the geological formations in Ohio it can be expected that there is a higher likelihood of acidic soils in eastern Ohio where the soils originated from sandstone and shale. Conversely, there is a lower likelihood of acidic soils in western Ohio where the soils originated from calcite-rich glacial deposits.
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:
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, vigor, and resilience of the lawn. If the pH drops further below 6, other nutrients can become more available such as boron and aluminum which are harmful to turfgrasses in excessive amounts. Fortunately, this issue is not a major concern in Ohio lawns.
It’s important to note that an excessively high (alkaline) soil pH (greater than 8.0) is just as undesirable as a low (acidic) pH. When the pH exceeds 8.0, nutrients such as nitrogen, phosphorus, iron, manganese, boron, copper, and zinc become less available for use by turfgrass plants. The result may be a less vigorous, thinning, and unhealthy lawn. Thus, over-application of liming products may cause the development of alkaline soil conditions. Alkaline soil in Kentucky bluegrass lawns are even known to cause a favorable environment for the development of summer patch disease, caused by a fungus that infects turfgrass roots.
The application of lime does not result in an immediate and dramatic change to soil pH levels or the health of turfgrass plants. Homeowners should expect that it may be several months before the soil pH changes. In addition, applications of lime should be made either in the spring or fall when rainfall is most abundant. Rain helps move the material into the soil profile and rootzone and also helps avoid any potential for turfgrass foliar burn or injury after application.
Is Liming Necessary?
The only way to determine whether or not liming is needed, and 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 can be obtained at a local garden center to test soil pH and determine the need for liming. These simple tests do not, however, calculate how much lime is needed to correct the acidic condition, and their accuracy may be affected by how well calibrated the meter is, as well as how comfortable the homeowner is with the procedures required for sampling. It’s important to understand that 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. The amount of lime required to raise soil pH to this level for a particular soil is designated as the “lime requirement” on soil test reports.
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 1,000 square feet. Since most liming products are not likely to be 100% pure calcium carbonate, one must calculate how much product to apply to the lawn. To do this, find the number on the bag’s label titled CALCIUM CARBONATE EQUIVALENT (it will be displayed as a percentage). Next, find the liming requirement in the soil test report. Using these two numbers, perform the following calculation:
Liming Requirement (from soil test) ÷ Calcium Carbonate Equivalent
= Amount Of Product per Acre or per 1,000 Square Feet
If the amount of product exceeds the values in Table 1, the amount recommended for your lawn should be divided in half and applied at two different times during the year.
How Often Should Lime Be Applied?
Lime should be applied only when soil testing indicates that it is needed. Yearly lime applications without performing a soil test are strongly discouraged because alkaline (high pH) conditions may develop.
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 lime off the turfgrass leaves. In addition, if coring is carried out prior to the lime application, it will help the lime incorporate into the soil.
Are All Liming Materials the Same?
As indicated in Table 1, 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 changes soil pH very little, if at all, and should never be considered as a liming material.
|Material||Calcium carbonate equivalent*||Rate of pH change||Max recommended rate of application**||Other comments|
|Burned lime||180||Fast||10||Hazardous, difficult to apply|
|Dolomitic limestone||70–95||Slow||50||Also a source of magnesium|
|Hydrated lime||140||Fast||20||Hazardous, difficult to apply|
|Pelletized limestone||70–95||Fast||50||Easy to apply, more expensive than other sources|
*These are approximate values and will vary with the purity of the individual product. **Maximum rate in pounds of product per 1,000 square feet. Multiply by 44 for the rate in pounds per acre.
pH - pH is the negative logarithm of the hydrogen ion concentration. A low or acidic pH (<7) has more hydrogen ions in solution compared to a high or basic pH >7.
Mullen, Robert, Lentz, Edwin, and Watson, Maurice. 2016. “Soil Acidity and Liming for Agricultural Production.” (AGF-505). Ohioline. The Ohio State University.
Schlossberg Maxim J., F. Clint Waltz Jr., Peter J. Landschoot, and Bradley S. Park. 2008. “Recent Mechanical Cultivation of Lawns Enhances Lime Application Efficacy.” Agronomy Journal Volume 100, Issue 3: 855–861. https://doi.org/10.2134/agronj2007.0256.