Definition

• Blossom end rot is a common occurrence in tomatoes. It appears on green, ripening and ripened fruits, but the first fruits to ripen are the most likely to show symptoms of the nutrient deficiency. The bottom of the fruits form black, sunken, wrinkled, tough spots that vary in size. The longer the fruit stays on the vine, the deeper and more pronounced the black rotted spot becomes.
  
  

Cause

• Blossom end rot is caused by a combination of environmental conditions. A lack of calcium and uneven or irregular watering exacerbate blossom end rot. Periods of drought while the tomato plant is developing fruit is a major contributing factor. Also, watering that is uneven and only allows a portion of the plant to receive sufficient water can contribute to blossom end rot. Inadequate fertilizing with micronutrients prevents the tomato plant from receiving enough calcium. Also root damage, excessive nitrogen and high levels of salt in the soil prevent the tomato plant from taking up enough calcium from the soil.
  
  

Prevention

• Prevention methods include proper cultivation of tomato plants. Tomato plants love water, especially during bouts of hot weather. Keep the soil evenly moist and do not allow the tomato plant to wilt between waterings. Use a fertilizing solution low in nitrogen but high in phosphorus, such as 4-12-4 or 5-20-5. If the fertilizes lacks micronutrients like calcium, apply an additional micronutrient solution. Allow tomato plants to develop deep, extensive root systems by giving them ample room to grow. Don't plant them too closely to other plants or use containers that are too small. One sign that a container is too small is that the tomato plant's roots wrap around and around, encircling the container. Allow the soil to become warm before planting tomato plants in the ground. Cold soils develop weak, small root systems incapable of soaking up adequate amounts of water. Spray young tomato transplants and seedlings with nutrient-dense seaweed extract to prevent nutrient deficiency.
  
  

Control

• Tomato plants suffering from blossom end rot may benefit from a calcium foliar spray. Follow the directions on the product label for application, because applying too frequently may damage the plant or inhibit the growth. Calcium foliage sprays are not sufficient means for regular calcium intake, so add high calcium lime to the soil. Implement a regular watering schedule that allows the soil to remain moist but not water-logged. Stop fertilizing with high nitrogen fertilizers and use the solutions recommended above.