If your plants are showing signs of calcium deficiency, a soil additive can supply the missing nutrient. However, sometimes low levels of calcium in the soil aren’t to blame for plants’ deficiency symptoms. Your soil could contain plenty of calcium, but it isn’t available to the plants. A soil test can indicate whether your soil would benefit from additional calcium and which additive is best. Dig the additive into the soil before planting your plants.
How to Add Calcium to Garden Soil
Limestone or gypsum supply your garden soil with calcium. If your soil is acidic, adding limestone helps boost most vegetable crops by increasing alkalinity. For example, if your soil pH is below 5.5, add 2 to 3 pounds of dolomitic lime per 100 square feet to raise the pH. Apply to your local cooperative extension office for a soil test to determine its pH. Add the lime two to three months before planting your vegetables or other plants to allow time for the it to dissolve into the soil. Dig the lime into the soil to a depth of about 6 inches, and water the soil afterward to the same depth.
For soils that have a pH of 6.5 to 6.7, gypsum is a better choice for adding calcium, because it doesn’t alter the soil’s pH. Before planting your plants, spread about 1 to 2 pounds of gypsum per 100 square feet, and dig it into the soil.
How Calcium Benefits Plants
Calcium is essential for the formation of roots, stems and new growth in plants. The nutrient forms calcium pectate, which plants use to construct cell walls and membranes. Consequently, calcium helps provide plants’ rigidity. Plants also use calcium to create carbohydrates like cellulose and starch. What’s more, calcium benefits your garden soil. It improves soil structure by helping soil particles stick together.
Calcium Deficiency in Plants
Symptoms of calcium deficiency in plants usually appear on new growth. The typical symptoms include stunted growth, distorted leaves and pale yellow patches between the leaf veins. The leaves may also be cupped. Weak stems, premature blossom and bud dropping, and dying stem and root tips are some more signs of calcium deficiency in plants. In certain vegetables like tomatoes (Lycopersicon esculentum_,_ hardy in U.S. Department of Agriculture plant hardiness zones 10 through 11), calcium deficiency causes a disorder called blossom end rot. A watery spot appears at the blossom end of the tomato, and the spot grows wider and darker as the fruit enlarges. Finally, the spot sinks or flattens, and the surface becomes firm.
Causes of Blossom End Rot
Blossom end rot can affect plants even when the soil they’re growing in contains plenty of calcium. The availability of calcium is affected by the presence of other minerals like magnesium, ammonium and potassium in the soil. If the soil contains an excess of other salts, calcium salts decrease in availability to plants. Similarly, excessively wet or dry soil can reduce the uptake of calcium by plant roots. The best method for assessing whether low levels of calcium are causing blossom end rot in your plants is to test the soil.