In both plant and animal life calcium is an essential element; it is found among other paces in bones, eggshells and seashells. Muscles and nerves do not function without calcium.
The name calcium comes from the Latin calx, calcis = stone. In its pure form it is a silver-looking metal, a bit harder than lead and easy to work. The metal ignites on heating and reacts violently with water and acids. Calcium is found all over the world; 3.64% of the Earth’s crust consists of calcium. The hardness of mains water is mostly caused by (the amount of) dissolved calcium salts.
Calcium is found throughout the plant and is needed for many processes in it, but the most important is for the growth process. It has a regulation effect in the cells and contributes to the stability of the plant.
Plants have two transport systems: the xylem and the phloem. Most nutrients can be moved around by either system, but not calcium. Since calcium is pretty much only transported via the xylem, in the plant it is a not very mobile element. This is why it is important that there is always sufficient calcium present is in the root environment, so that it is continuously available for uptake by the plant.
Calcium is moved around in the plant by the upward sap stream. In cases of calcium deficiency it is the older leaves that show the first symptoms. It is usually not the very lowest leaves but those just above them (as in a magnesium deficiency, see cAnna’s info on Magnesium Deficiency). A calcium shortage is recognisable by the presence of yellow/ brown flecks on the leaves, often surrounded by a sharply defined brown edge. Also symptomatic are a stunted growth rate, and in the serious cases smaller, loose-growing buds. One can guess the result: a strikingly reduced yield.
The progression of calcium deficiency in chronological order.
A shortage of calcium can come about due to:
What to do
Lime in a free state is quickly taken up by the plant. Because lime is not very mobile in the plant the symptoms in the older leaves will not disappear. But normal development will be reassumed without any signs that there was a deficiency.
In addition to problems caused by a calcium shortage in the plant, there can also be trouble as a result of a shortage of calcium in the soil. Calcium shortages in the soil often accompany acidification of the soil. In an acidic root environment, among other things phosphate becomes less freely available to the plant and a number of heavy metals become more available for it, which can lead to poisoning of the plant (by for instance aluminium, manganese, nickel).
Too much calcium is damaging to the plant and usually has a retarding effect on the growth and leads to a darker coloured plant as a result. An excess of calcium can also lead to boron, manganese, zinc, magnesium, and sometimes copper deficiencies.