Along with magnesium and sulfur, calcium is one of the three secondary nutrients. Like primary nutrients (nitrogen, phosphorus and potassium), those elements are essential for healthy plant growth. However, they are needed in lesser amounts.
Function of Calcium
Calcium, in the form of calcium pectate, is responsible for holding together the cell walls of plants. When calcium is deficient, new tissue such as root tips, young leaves, and shoot tips often exhibit distorted growth from improper cell wall formation. Calcium is also used in activating certain enzymes and to send signals that coordinate certain cellular activities.
Calcium is not mobile within the plant. So the plant relies on the process of transpiration in which the plant roots take up the soil solution (which contains the needed calcium), transports it to new growth where the calcium is used and the excess water vapor escapes out through holes in the leaves called stomata. Anything that slows transpiration, such as high humidity or cold temperatures, can induce calcium deficiency even if the calcium levels are normal in the growing medium. Parts of the plant that transpire little water, i.e. young leaves and fruit, will display calcium deficiencies first. Blossom end rot of tomatoes is a classic case of calcium deficiency. Calcium deficiency can arise if levels in the fertilizer solution are less than 40-60 ppm and/or potassium, magnesium, or sodium levels are too high.
“Calcium deficiency causing leaf edge necrosis in poinsettias.”