Autumn right time to adjust soil pH for lawn, garden

Date published: 11/6/2009

SOIL pH is an environmental condition that affects plant growth. I frequently recommend doing soil tests and applying lime to correct low-pH, or acidic, soil conditions. Looking at various products and materials and how they raise or lower soil pH may help you decide the best strategy for your garden or lawn.

Soil pH is influenced by several factors. The first is the type of rock the soil was formed from. Soils formed from alkaline rocks will generally have higher pH values than soils formed from acidic rocks. Rainwater will leach basic nutrients such as calcium and magnesium from the soil, and they are replaced by acidic elements such as aluminum and iron.

The use of chemical fertilizers containing ammonium and urea turns the soil acidic more quickly. Decomposing organic material also adds to soil acidity.

Lime, made from ground limestone, is commonly used to increase soil pH. It contains calcium and/or magnesium compounds that neutralize soil acidity. Lime is commonly available as ground, pulverized or pelletized products.

Particle size is a key factor in how fast lime will react and increase the soil pH. Finely ground limestone, the powdery variety, works fastest to reduce soil acidity, while larger particles will do the job more gradually over time.

So what is the right lime particle size to buy? Research has shown that the fine, or "100-mesh," particles can be expected to react rapidly and increase pH more quickly than larger particles. Where pH is very low and fast correction is desired, use a lime product containing a larger percentage of 100-mesh particles in the product.

Pelletized lime is finely ground limestone that has been formed into pellets about two-tenths of an inch in diameter by using a binding agent. The pellets spread more easily and are less dusty than ground or pulverized lime products. The pellets then break down rapidly when they come in contact with soil moisture, and neutralize soil acidity in the areas surrounding the pellets.

Research shows that pelletized lime is less effective in raising the pH of very acidic soil because the particles dissolve in localized areas. But it is very effective in maintaining soil pH at optimum levels when a regular liming program is used to keep soil pH above 6.0.

John E. Howe is an agent in Virginia Cooperative Extension's Spotsylvania County office specializing in animal science. Phone 540/507-7571; e-mail jhowe@vt.edu.

Follow us on

Date published: 11/6/2009