Does Calcium Affect Soil pH?

Plants and Calcium

• Just as people and animals need calcium for strong bones and teeth, plants also use calcium to build strong cell walls, which helps to give them shape. Calcium also helps cells to divide and grow, allows materials to cross the cell membrane and assists with metabolic processes. About 3.6 percent of the Earth's crust consists of calcium, and it occurs abundantly in most garden soils. Calcium ions cling tightly to clay soil and particles of organic matter, making calcium available to plants to take in through their roots.

Plants and pH

• Soil pH can have a profound effect on your plants' growth and can determine whether a plant succeeds or fails in your garden. Most plants grow best at a neutral pH of about 6.5 to 7.0, although a few species like blueberries and rhododendrons prefer a low or acidic pH. Extremes in pH can create nutrient deficiencies or excesses to the point of toxicity, so you should use care when applying any material, like lime or another form of calcium, that could cause drastic changes in pH.

Lime and pH

• Calcium raises soil pH and is used to correct acidic soils. There are multiple forms of limestone and other liming materials, calcium-containing substances that increase the soil pH. Which you choose will depend on the needs of your soil. For example, dolomitic limestone contains magnesium as well as calcium, making it a good choice for soils low in magnesium. Wood ashes act as a liming material and contain magnesium and potassium in addition to calcium. You must know the pH of your soil before applying a liming material so that you don't raise the pH too high. In alkaline or high-pH soils, most trace elements become unavailable, and plants suffer from deficiencies in phosphorus, one of the most important nutrients for plant growth. A routine soil test will tell you not only the pH of your soil but how much lime you need to add to achieve a neutral pH.

Applying Lime and Calcium

• Spread the recommended quantity of lime evenly over the surface of your garden soil. Although surface-applied lime will raise the pH to a depth of about 3 inches, for maximum efficacy, you should incorporate the lime into the top few inches of soil. To provide your plants with extra calcium without adding lime, add crushed eggshells to the planting hole or sidedress existing plantings. Calcium deficiencies can cause blossom-end rot in plants like tomato and pepper.