It's often necessary to apply agricultural limestone to raise soil pH into a desirable range for the best plant growth.
However, some plants, such as Azaleas and Rhododendrons, prefer an acidic soil and don't respond well to liming.
As a general rule, most lawns and plants prefer a soil pH that is close to neutral in the 6.5 to 7.2 pH range, with a pH of 7.0 being neutral.
Excerpts from our soil pH page:
pH is referred to as the "acidity" of the soil and is measured by the number of Hydrogen ions present in the soil solution. Since S.W. Pennsylvania receives considerable rainfall every year, and since rain is H2O, soils tend to revert back to an "acid condition." Ammonium fertilizers also have an acidifying effect on the soil.
When the soil pH is too "acidic" (low pH) or "alkaline" (high pH), nutrients present in the soil become locked-up or unavailable. Correcting the pH has the same effect as applying fertilizer since it "unlocks" plant nutrients that are already present.
Most plants grow best within a pH range of 6.5 to 7.2 (7.0 is neutral). The best way to find out what your soil needs is by sending a sample to a soil lab.
The soils I've tested in the South Hills of Pittsburgh and Washington County over the past 20 years usually need lime and phosphorus. The exception would be soils located in "bottom ground" (near streams and rivers) which usually don't require lime. Of those soils requiring lime, dolomitic lime (high in magnesium) usually fits the test recommendations best.
Generally speaking, the finer the particle size of lime the faster it will have an affect on soil pH. Particle size is indicated on the label as what percentage will pass through a certain "mesh" size.
Some lime products are powders that are turned into pellets for ease of application and much less mess. We use and recommend this form of lime.
Lime powders, while less expensive than pelletized products, can be very messy and difficult to spread. Many have a "dusty" consistency like that of baking flour.
There are several types of lime available but we recommend only using the less caustic agricultural forms of lime such as Dolomite Lime or Calcium Carbonate. Remember that 'pelletized' products are much easier to apply.
The most commonly available and least expensive lime product is probably Calcium Carbonate in the powder form.
In addition to containing Calcium, dolomitic lime also contains a higher percentage of Magnesium than calcitic limestone. If calcium and magnesium levels are low, use this type of lime.
Both types are generally considered unsatisfactory for use on lawn areas. If used for other applications, be sure to read and follow label instructions.
The CCE provides a yardstick for comparison of various lime products. Limestone recommendations are based on a neutralizing action equal to 100% calcium carbonate limestone. Use the formula below for calculating the amount of lime to use.
AMOUNT OF LIME REQUIRED EQUALS:
CCE of Lime Material
Lime moves downward through the soil profile very slowly so it is best to mix recommended amounts with the soil using a rototiller or similar machine.
When applying lime to an established lawn, it is beneficial to apply lime in conjunction with core aeration, using a machine that pulls out soil plugs.
General recommendations call for separating lime applications from fertilizer applications by at least two weeks.
Even though fall is often prescribed as the ideal time of the year to lime, due to the freezing and thawing action of soil over winter, lime can actually be applied anytime of the year.