Calcium deficiency isn’t common, and can be difficult to diagnose, but is responsible for two main disorders – blossom end rot in tomatoes and bitter pit in apples.
- Localised tissue necrosis and death
- Brown, dead margins on young leaves
- Leaf curling
- Stunted growth
- Blossom end rot – roughly circular black or brown patches at the bottom of tomato fruit
- Bitter pit – sunken pits and dark spots on the skin and in the fruit of apples
What is calcium deficiency?
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.
What does it affect?
- All plants can be affected, but especially
How to prevent calcium deficiency
Grow plants as well as possible, so they never go short of water. The soil or compost should be kept consistently moist, never allowing it to dry out, without cycles of drying out followed by overwatering.
Make sure soils contain lots of bulky organic matter to hold soil moisture. Covering the soil with a 5-7.5cm (2-3in) thick mulch will help conserve moisture.
Adding garden lime to acidic soils to increase the pH (alkalinity) to around 6.5 will help; obviously, this is not suitable for acid-loving/lime-hating plants.
Feed with a general-purpose, balanced fertiliser, such as Growmore, and avoid excessive use of nitrogen-rich fertilisers.
Foliar sprays of calcium nitrate may help increase calcium within the plants, and can be particularly effective to prevent bitter pit.
- Garden lime
- Calcium nitrate