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.
How do I know IF my lawn needs lime?
How do I decide how much lime to apply?
How often should I apply lime?
What is the best time of the year to apply lime?
Are all liming materials the same?
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.
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.
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. The amount of lime for a particular soil is designated as the LIME REQUIREMENT on soil test reports.
A soil test report 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 that information perform the following calculation:
LIMING REQUIREMENT (FROM SOIL TEST) X 100 = AMOUNT OF PRODUCT/ACRE CALCIUM CARBONATE EQUIVALENT or /1000 SQUARE FEET
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.
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.