How to prevent Blossom end rot



Blossom end rot

Blossom end rot

What is Blossom-End Rot?

Blossom end rot is not a disease but rather a physiological disorder which is caused by a calcium imbalance within a plant.

How to identify Blossom end rot

  • Blossom-end rot looks like a discoloured, watery, sunken spot at the blossom end of the fruit, most commonly tomatoes.
  • The spot will start out small, and grow larger and darker as the fruit continues to grow.
  • Calcium Deficiency in garden plants can also cause yellowing, pale and curling leaves, and stunted growth.


Crops affected by Blossom end rot

Nightshades such as:

  • Tomatoes, eggplant and pepper as well as curcubits and melons are more prone to blossom end rot than other crops.

Causes of Blossom end rot

  • Blossom end rot is caused by a calcium deficiency.
  • When the soil pH is too acidic (low pH) or alkaline (high pH), nutrients present in the soil become locked-up or unavailable.
  • Excessive fertilizer, particularly high nitrogen fertilizer is another cause. Too much nitrogen promotes the development of foliage and rapid vertical growth. The plant will actually grow faster that the calcium is able to circulate, hence it is unavailable where needed.
  • Irregular watering and fluctuating moisture - drought and over saturation - will also reduce calcium uptake into the plant.

How to control Blossom end rot

  • Remove the affected fruit. There is not much that can be done once the rot sets in. If the affected fruit is pinched off, the plant might blossom again and set normal fruit.
  • Apply a liquid calcium fertilizer after removing the affected fruit.
  • Correct soil pH -Most vegetables 6.2 to 6.8 is the range needed to free sufficient calcium into the soil chemistry. If the pH is too low you'll want to add lime to the soil which not only frees up available calcium by adjusting the pH - but also contains calcium which increases levels in the soil.
  • Sprays such as Rot Stop can be applied weekly or bi-weekly. Most of these sprays are not a long-term fix, but can help to salvage a crop until long term measures kick in.

How to prevent Blossom end rot

  • Maintain a soil pH of around 6.5 on the pH scale. Liming the soil can help increase the ratio of calcium ions to other competitive ions in the soil. During transplanting you can also add crushed eggshells, gypsum, or bone meal to the hole to fortify calcium intake.
  • By ensuring uniform moisture supply, through use of mulches and/ irrigation to avoid drought stress. In places where there is a lot of rain ensure good drainage around the plants.
  • Avoid damaging plant roots by cultivating too close to the plant roots
  • By use of nitrate nitrogen instead of ammoniacal nitrogen fertiliser. Ammonical nitrogen increases the chances of blossom end root.
  • Apply correct amount of fertiliser during early fruiting, this is when blossom end root is more likely to occur (soil testing is important).



Nyaladzi Onneile Jacob
Farm Products Crop Scientist
Bsc.Crop Science & HD Forestry and Range Ecology