Does Lime Raise or Lower Soil pH?

pH Scale

• The pH scale is used to determine a soil's alkalinity and acidity. Acid soils have a pH level of 6.9 or less. Alkaline soils have a pH level of 7.1 or more. A pH reading of 7 is neutral. Knowing your soil's acidity and alkalinity is important, because the pH interacts with different soil minerals and nutrients, which can affect a plant's growth rate and vigor. Highly acidic soils, or those with numbers lower than 7 on the pH scale, make minerals like copper and aluminum unavailable to plants; alkaline soils, or those above 7 on the pH scale, can sometimes make these minerals available to the point of toxicity. Not all plants do best in neutral soils. Rhododendrons and azaleas, blueberries, cranberries and some oak trees thrive in slightly acidic conditions. Test your soil before adding any lime or other amendments. Soil testing allows you to provide the best quantities of lime for your soil and your crop.

Liming Rates

• Sandy soils tend toward alkalinity, while heavy, compacted soils tend toward high acid levels. Factors that contribute to the pH level are soil texture, the amount of organic matter present and the underlying soil particle composition. Soil composed of limestone, for instance, is more inclined toward alkalinity. Soil tests measure the soil's baseline pH level. They also measure the soil's resistance to a change in pH. High amounts of organic matter resist pH changes, resulting in the need for higher amendment quantities in highly organic soils. Soil scientists use a formula measuring for the baseline and the amount of resistance to change. The results are the recommended liming rates for your garden's soil. Going against recommendations can damage soil structure by reducing a healthy acid level to poor, alkaline soil.

Types of Lime

• The type of lime used depends upon liming recommendations, type of soil and your preferences. Lime products are available from garden centers, nurseries and other retail locations that sell garden products. Aglime is used for agricultural purposes. Like all liming materials, it is composed of calcium and magnesium compounds, which work together to reduce soil acidity. Dolomitic lime, calcitic lime, burnt lime, slaked lime and marl are some commonly used lime compounds. Lime is available in lesser amounts in oyster shells, cement kiln dust and wood ashes. The type of lime to use in your soil depends upon the amount of lime needed to bring your soil's pH into balance.

Considerations

• Soil scientists from Rutgers University in New Jersey explain that overliming is a frequent cause of alkaline soil and results from annual liming without the benefit of soil test recommendations. Soil tests do not need to be taken annually. Instead, test your soil when your plants appear lackluster and their growth and harvest yields are in decline.