Blossom End Rot on Tomatoes

All you need to know about Blossom End Rot, dont let your plants dry out!

 Here is all the information that you need about Blossom End Rot on tomatoes. However before you try adding calcium etc to your soil it is worth nothing that there is normally not a deficiency of calcium in the soil as 90% of the times I have had Blossom End Rot is in hot weather and I have let the compost or soil dry out that bit too much. It happens easier if you are growing in post of peat bags. When the Blossom End Rot appears it is usually a few days after the soil has dried out, so although your soil might seem OK, it might not have been a few days before. 


Blossom-end rot (BER) is generally thought to be triggered by a localized calcium deficiency in the blossom end of the fruit.  It often occurs when dry soil conditions reduce the amount of water movement into the plant, interrupting the movement of calcium to the fruit, so it is not lack of calcium in the soil.  Calcium is an important component of cell development.  Therefore BER is caused primarily by dry soil conditions, not by a deficiency of calcium in the soil or plant.


 A small water-soaked or light brown area appears around the blossom-end of the tomato when the fruit is green or just ripening.  The lesion darkens and enlarges rapidly, becoming sunken and black.  It may affect over half of the fruit. 

Soil or foliar applied calcium has not been shown to be effective in preventing BER.  Foliar-applied calcium is taken up and fixed in the leaves, and very little reaches the fruit.

Besides moisture, many other factors seem to influence BER as well.  In fact, there is now some thought that low calcium levels in the fruit are not the trigger for blossom-end rot at all.

 The list of factors that could influence blossom-end rot:

     High temperatures and intense sunlight, especially following cooler, overcast weather;

    High ammonium-nitrogen levels in the soil,

    High salinity;

    Stress factors, such as dry conditions, that reduce fruit growth;

    Stress occurring during periods of rapid fruit growth;

    Potassium/calcium ratios in the fruit;

    High nitrogen levels;

 There is now speculation that stress-free, rapid growth conditions create the susceptibility for blossom-end rot in fruit at a certain stage of development.  If conditions suddenly turn stressful, reducing growth rates, blossom-end rot is thought likely to develop.