Calcium deficiency

Calcium deficiency (known as blossom end rot when symptoms show on tomato fruit and tip burn on plant leaves) is a plant disorder that can be caused by insufficient calcium in the growing medium, but is more frequently a product of low transpiration of the whole plant or more commonly the affected tissue. Plants are susceptible to such localised calcium defieciences in low or non transpiring tissues because calcium is not transported in the phloem. This may be due to water shortages, which slow the transportation of calcium to the plant, or can be caused by excessive usage of potassium or nitrogen fertilizers.

When the plant is left too dry it struggles to move calcium around to the fruit and will take it instead to the foliage first, leaving a lack of calcium within the fruit, hence the problem. In simplistic terms the plant is taking action to save itself and in so doing is prepared to abort the fruit.

Calcium deficiency is one of the main causes of cavity spot in carrots.

Symptoms
Calcium deficiency symptoms appear initially as localised tissue necrosis leading to stunted plant growth, necrotic leaf margins on young leaves or curling of the leaves, and eventual death of terminal buds and root tips. Generally the new growth and rapidly growing tissues of the plant are affected first. The mature leaves are rarely if ever affected because calcium accumualates to high concentrations in older leaves.

Cabbage and Brussels sprout
Internal browning. Exhibits characteristic "tip burn" at tips/edges of the leaf. Leaves are deformed and cabbage head will not form if supplemental calcium is not applied. Cupping of leaves is typical.

Carrot
Cavity spot - oval spots develop into craters which may be invaded by other disease causing organisms.

Tomatoes and Peppers
Blossom end rot - Developing fruit show a black area on the bottom of the fruit, beginning opposite the stalk. This area is often infected by other bacteria.

Treatment
Calcium deficiency can sometimes be rectified by adding Agricultural lime to acid soils, aiming at a pH of 6.5, unless the plant in question specifically prefers acidic soil. Organic matter should be added to the soil in order to improve its moisture-retaining capacity. However because of the nature of the disorder (ie poor transport of calcium to low transpiring tissues) the problem cannot generally be cured by the addition of calcium to the roots. In some species the problem can be reduced by prophylactic spraying with calcium chloride of tissues at risk.

Prevention
The primary cause of calcium deficiency is not a low calcium content in the soil, but infrequent watering, which inhibits the plant from transporting calcium from the soil. Ensure watering is frequent, but do not overwater. If watering is not the issue; add a level teaspoon of Calcium Nitrate to a gallon of water and add about a pint to each plant once every 10 days or so.

Tomatoes
The problem is commonly caused when growing in growbags as there is they often leave little room for a large root system, and without drainage holes in the bottom will cause either over- or under-watering very easily. Avoid growing more than 2 plants in one bag. Plant tomatoes into open-bottomed pots and place pots in contact with growbag compost so roots can travel between them. Water regularly, but in small amounts, especially during prolonged periods of hot, dry weather.