Causes

• Poor root system development could cause blossom end rot even in soil with adequate calcium. Planting tomatoes in cold soil too early in the season stunts roots and interferes with the flow of water to the upper parts of the plant. Too much water or too little water also affects the ability of the tomato to supply soil calcium to its developing fruit. When these different problems combine, calcium deficiencies in the plant trigger blossom end rot. Correcting water supply fluctuations could solve the problem without adding calcium to the garden.
  
  

Treatments

• Calcium chloride solution sprayed on the tomato plant's leaves supplies extra calcium when soil tests show a lack of that mineral. Dissolving 4 tsp. of calcium chloride in 1 gallon of water creates a calcium-rich spray for direct feeding of the plant. Spraying once a week for four weeks deposits enough calcium to compensate for soil deficiencies. Spraying more than four times could burn leaves. Calcium chloride sprays may not stop blossom end rot caused by poor gardening methods.
  
  

Fertilizer Choices

• High-nitrogen ammonia fertilizers interfere with calcium uptake, but nitrate fertilizers supply adequate nitrogen without causing the mineral imbalance. Applying a 4-12-4 N-P-K fertilizer helps balance nutrients in the soil for tomatoes. This formula supplies more superphosphate and less nitrogen during critical early growth and decreases blossom end rot problems, according to Vegetable MD Online.
  
  

Precautions

• Preparing the soil correctly and following good cultural practices prevents most blossom end rot problems. Test the soil in the fall and add lime to the garden to correct any calcium deficiency. Break up heavy clay soils by tilling in organic material. Transplant tomatoes to the garden only after soil warms and water plants at a rate of 1 inch per week. Strive for a constant supply of soil moisture, protecting the upper layers of soil with 3 inches of mulch.