Along with magnesium and sulfurcalcium is one of the three secondary macronutrients. Like the primary macronutrients (nitrogen, phosphorus, and potassium), these elements are also essential for healthy plant growth, granted in slightly lesser amounts.

Functions of Calcium

Calcium, in the form of calcium pectate, is responsible for contributing to the building of cell walls in plants. When calcium is deficient, new tissue such as root tips, young leaves, and shoot tips often have improper cell wall formation causing visual distortion in new growth. Calcium is also used in activating certain enzymes and sending signals that coordinate certain cellular activities.

Calcium Deficiency

Calcium is not mobile within the plant. Therefore, the plant relies on the process of transpiration in which the plant roots take up the soil solution (which should include needed calcium), transports it to new growth where the calcium is used and the excess water vapor escapes 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.

Calcium deficiency causing leaf edge necrosis in poinsettias by PRO-MIX Greenhouse Growing.
Calcium deficiency causing leaf edge necrosis in poinsettias.

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 blossom end rot of tomatoes by PRO-MIX Greenhouse Growing.
Calcium deficiency causing blossom end rot in tomatoes.

Calcium Toxicity

Calcium toxicity rarely occurs. High levels of calcium can compete with magnesium and potassium uptake, causing their deficiencies.

Calcium Source - Fertilizer

Most fertilizers do not contain calcium, so it is important to read the label. Some fertilizers list the percentage of calcium and magnesium in the fertilizer analysis, e.g. 15-7-14-3Ca-1Mg, while others are identified as a “Cal-Mag”, calcium-magnesium containing fertilizer such as 15-5-15, 17-5-17, etc. If you are not certain that a fertilizer contains calcium, check the “guaranteed analysis” on the fertilizer label as it lists the percentage of each element in the fertilizer.

Most calcium-containing fertilizers are formulated with calcium nitrate. Keep in mind that calcium nitrate is potentially basic, meaning it will cause the pH of the growing medium to rise unless acid is injected, or potentially acidic fertilizers are used in rotation.

Calcium Source - Water

All water sources supply some calcium. As a rule, water coming from deep wells or most non-coastal regions of North America has sufficient calcium for normal crop growth. However, water from a shallow well, coastal region, rain, lake, river, or pond generally has insufficient calcium levels.

Regardless, it is best to have your water tested to verify if your water is supplying sufficient calcium. If the calcium level in your water is 40-60 ppm or more, then there is little need to use a fertilizer that provides calcium.

If calcium levels in your water are less than 40-60 ppm calcium, talk with your Premier Tech Grower Services representative and together, a customized fertilization program can be developed to fit your specific crop’s needs.