Fertilizers replenish soil nutrients that plants draw out in order to live. Among the many nutrients that plants take from the soil, calcium provides many essential functions, and calcium deficiencies can cause noticeable problems in your garden. Repairing a calcium deficiency is as simple as incorporating a calcium source into the soil as part of your soil fertilization program.
Among many functions, calcium strengthens the plant's cell wall, providing extra strength and support to the plant. It acts as a carrier molecule, transporting other essential compounds and nutrients in and out of the cell. Finally, calcium helps to neutralize naturally occurring acids inside of the plant.
Calcium naturally forms in soil from lime, gypsum and superphosphate. In synthetic fertilizers, it is available in calcium ammonium nitrate and calcium nitrate, both of which also provide nitrogen. Organic sources of calcium that can be applied as fertilizers include eggshells, bone meal, limestone and gypsum.
According to the Michigan State University Extension, it is difficult to over-apply calcium to plants. Calcium is available as a foliar spray or a dry fertilizer. Foliar sprays should be applied to new plant growth, as older growth cannot absorb and will not benefit from the calcium. When applying a calcium-containing fertilizer to the soil, always follow the directions on the package, as other nutrients the fertilizer contains may harm your plants or the environment if overused. "Rodale's Ultimate Encyclopedia of Organic Gardening" recommends using an organic calcium supplement when transplanting seedlings, especially tomatoes and peppers, by adding a handful of bone meal or crushed eggshells to the hole before transplanting.
Plants deficient in calcium first show stunted growth in new leaves and roots. Young leaves may appear distorted, yellowish, and develop spots or irregular leaf margins. Several vegetable disorders originate from calcium deficiencies. Blossom-end rot afflicts tomatoes and peppers, and the blossom end of the fruit develops a leathery, rotten-looking patch. Calcium deficiencies also cause blackheart in celery, cavity spot in carrots, and internal tip burn in cabbage. If you observe these signs in your plants, you may need to provide more calcium.
Plants absorb calcium in water, so dry conditions often produce the symptoms of calcium deficiencies, even when the soil contains adequate calcium. In these cases, providing ample water will make calcium available again to the plant. Furthermore, calcium exists in a balance with potassium and magnesium, so an imbalance in one may affect the other three.