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.
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
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.
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.
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.
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.
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:
Requirement (from soil test) Calcium Carbonate Equivalent = Amount
Of Product/Acre or /1000 Square Feet
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.
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.
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
Materials And Their Characteristics
carbonate equivalent *
of pH change
recommended rate of application **
difficult to apply
a source of magnesium
difficult to apply
to apply, more expensive than other sources
*These are approximate values and will vary with the purity of the
**Maximum rate in pounds of product/1000 square feet. Multiply by
44 for rate in pounds/acre.
from John R. Street and Susan K. White, Ohio State University Extension,