Calcium (Ca) is one of the macronutrients, needed by plants in relatively large amounts. Calcium deficiency can be caused by insufficient calcium in the growing medium (soil or compost), but is more often a result of poor movement of water in the plant or the affected tissues. This may be due to water shortages at the roots, irregular watering, poor water movement throughout the plant, or even too much nitrogen or phosphorous in the soil or compost.
Alkaline soils and soils or composts watered with alkaline (“hard”) water will contain good levels of calcium. Acidic, sandy and coarse soils, on the other hand, often contain poor levels of calcium.
General symptoms of calcium deficiency – localised tissue death, dead leaf margins and curling leaves – usually appear on new or young growth; mature leaves are rarely affected.
Calcium deficiency is responsible for two major disorders – blossom end rot in tomatoes and bitter pit in apples.
Apple bitter pit results in sunken pits and dark spots appearing on the skin and underlying brown, dry areas in the flesh of the fruit. The fruit may have a bitter taste. Some varieties are more susceptible than others – ‘Bramley’s Seedling’ being commonly affected. Affected fruit can still be eaten once the brown, bitter areas are cut out; they tend to be fairly superficial. It is often worse in hot, dry summers, which result in dry soils and restricted water uptake by the roots.
Calcium deficiency can also cause internal browning and leaf tip burn on some brassicas – especially Brussels sprouts, cabbages and cauliflowers – and oval spots that develop into cavities on carrots.
