Article 123 : Blossom End Rot

CALCIUM UPTAKE IN PLANTS AND BLOSSOM END ROT

by Carol Ann Harlos

Calcium is an important plant nutrient. It increases the strength of cell walls and decreases a plant’s susceptibility to disease pathogens. It is called a “macro” nutrient along with nitrogen, phosphorus, magnesium, potassium and sulfur.
It is not uncommon to hear gardeners complain about blossom end rot especially in tomatoes, cucumbers, peppers, squash, and melons. One is told there is a calcium deficiency or the soil was too cold or the plants were over watered. The condition is usually temporary. Gardeners ask “Why calcium?” Great question!

The roots of plants take up most nutrients which are dissolved in water. This involves the expenditure of energy by the plant. However the uptake of calcium is different. Its uptake is passive and does not involve the plant’s using energy. During the process of transpiration the water movement through a plant is due to evaporation from leaves, stems, and flowers. (You may have seen droplets of water on plants during a dry day.) Most of the water taken up by plants, up to 99%, is lost this way! Calcium is unique as transpiration is the only way it gets into the plant!

Think about it. This explains why plants that are in cool soil (planted too early in the season), or subjected to damp cloudy days, or are over watered, frequently have a calcium deficiency leading to blossom end rot, leaf necrosis, stunted growth, leaf curling. Transpiration stops and the newest growth is affected.

Sometimes folks will say they gave the plants extra calcium and the problems disappeared. What actually happens is that with increasing temperatures later in the season more transpiration occurred and more calcium was pulled up into the plant. Interesting, yes?

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Last updated October 16, 2019