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What is Blossom End Rot?

• Blossom end rot is a condition that causes the bottom of the tomato to turn gray and rot, leaving most or all of the fruit inedible. The rotten portion may be a small dot, or it may consume most of the tomato. Blossom end rot most often affects the first batch of fruit the plant produces.
  
  

Symptoms

• Blossom end rot usually begins to appear when the tomato is one-third to one-half its final size and still green.
  
  An early symptom is a dark, water-soaked area at the bottom of the tomato. This often goes unnoticed. The skin of the tomato soon begins to turn gray and look leathery, with concentric rings emanating from the original blossom. The good part of the fruit will still ripen and turn red, but the affected portion will remain gray.
  
  

Causes

• Blossom end rot is caused by a calcium deficiency in the plant. Calcium content in the soil can be compromised by inconsistent watering or overfertilizing. It is also possible that your soil simply does not contain enough calcium to support a tomato plant.
  
  The first group of tomatoes a plant grows are most likely to be affected because the plant's rapid growth demands a larger amount of calcium. Once it has reached its full size, the calcium level is easier to maintain.
  
  Confining or damaging the roots of the plant can keep it from absorbing enough calcium. Overpruning also contributes to blossom end rot.
  
  

Treatment

• Once blossom end rot strikes a tomato, it cannot be cured. This condition is physiological, meaning fungicides and insecticides will not help. Fortunately, it also cannot be passed from one tomato to another. Correcting poor gardening habits will keep the same plant from yielding more rotten tomatoes.
  
  Calcium sprays can be applied to the leaves of a plant to ensure that future tomatoes will be healthy. The fruit itself cannot absorb the spray, so existing tomatoes will not be affected. The University of Georgia's Agricultural and Environmental Sciences Department suggests mixing 4 tablespoons of calcium chloride with 1 gallon of water and spraying the leaves of the tomato plant liberally. This should be repeated every seven to 10 days until four treatments are completed.
  
  

Prevention

• Several months before planting, spread lime over the soil to replenish calcium content. Use mulch around the base of the plant.
  
  Avoid planting early in the season. Planting in cold soil contributes to blossom end rot. Waiting until after the last hard frost of the year is essential. This is difficult to predict, so waiting longer is safer.
  
  Maintain good watering habits. Tomato plants should get the equivalent of 1 inch of moisture per week from rain and manual watering combined.