Many homeowners believe applications of lime to the home lawn are necessary to maintain a high quality lawn. Few individuals, however, have a complete understanding of why lime is applied, how to determine if liming is needed, and how one should go about applying lime to the lawn. Also, most homeowners are not aware of the potential negatives of creating a pH too high by excessive application of lime.
Questions often asked about liming include:
This fact sheet will briefly discuss the important role that liming can play in the production of a healthy home lawn and then will address the above questions.
WHY HOME LAWNS NEED LIME. Lime is applied to soil, including that of home lawns, for the purpose of increasing the pH of the soil. Soil pH, a measure of the soil's acidity or alkalinity, governs the availability of many soil nutrients and 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. For turfgrasses used in Ohio home lawns, a soil pH of between 6.0 and 7.0 (slightly acidic) is ideal.
Several factors are responsible for 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 turfs. 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 the following: 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 lime to neutralize the acidic condition and 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.
It should be noted that an excessively high (alkaline) soil pH (greater than 8.01 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.
HOW TO DETERMINE IF LIMING IS 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 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. The reason is that individual soils can differ greatly in the amount of lime required to raise the pH to some 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.
HOW MUCH LIME TO APPLY? Most soil test reports will indicate the lime requirement in pounds of PURE calcium carbonate per acre, or per 1000 square feet. Since the liming product that you purchase is not likely to be pure calcium carbonate, you will have to calculate how much product to apply to your lawn. To do this, first 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) X 100 = AMOUNT OF PRODUCT/ACRE CALCIUM CARBONATE EQUIVALENT 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.
HOW OFTEN SHOULD LIME BE APPLIED? Lime should be applied ONLY when soil testing indicates that it is needed. Yearly applications of lime, without making a soil test, are strongly discouraged because alkaline (high pH) conditions may develop.
WHAT IS THE BEST TIME OF THE YEAR 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. It should be noted 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!
SOME LIMING MATERIALS AND THEIR CHARACTERISTICS | ||||
|---|---|---|---|---|
| Material | Calcium Carbonate equivalent* | Rate of pH change | Maximum 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 |
| Ground limestone | 70-95 | Slow | 50 | - |
| Hydrated lime | 140 | Fast | 20 | Hazardous, difficult to apply |
| Pelletized | 70-95 | Fast | 50 | Easy to apply; more expensive than other sources |
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*These are approximate values and will vary with the purity of the individual product. **Maximum rate in pounds of product/lOOO square feet. Multiply by 44 for rate in pounds/acre. | ||||
Prepared by:
William E. Pound
Extension Agronomist
John R. Street
Extension Agronomist
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Keith L. Smith, Associate Vice President for Ag. Adm. and Director, OSU Extension.
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