Blossom-End Rot

Blossom-end rot on tomato plant

Credit: Catherine Boeckmann
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Here are tips on how to identify, control, and prevent blossom-end rot on your tomatoes and garden plants.

What is Blossom-End Rot?

This is a common problem on tomatoes and eggplant caused by a low concentration of calcium in the fruit.  (Calcium is needed for normal cell growth.) Blossom-end rot usually occurs when there are wide fluctuations of moisture—which reduce uptake and movement of calcium into the plant. When the demand for calcium exceeds supply, the tissues break down.

How to Identify Blossom-End Rot

Usually blossom-end rot occurs when the fruit is green or ripening. It starts with a small, depressed, water-soaked area on the blossom end of the fruit.  As the spot enlarges, it becomes sunken and turns black or dark brown in color.

How to Identify Blossom-End Rot

  • Remove the affected fruit. There is not much that can be done.
  • The key is soil preparation. Maintain a soil pH around 6.5. Lime with supply calcium and increase the ratio of calcium ions to other competitive ions in the soil. Add crushed eggshells, gypsum, or bone meal to the transplant hole to fortify calcium intake. 
  • Maintain a more uniform moisture supply. Use mulches and/or irrigation to avoid drought stress. If it's rainy, ensure plants have good drainage and soil dries out (but do not cease to water). Overall, plants needs about once inch of moisture per week.
  • Avoid cultivating, or hoeing, near the roots of tomato plants. 
  • For fertilizer, use nitrate nitrogen not ammoniacal nitrogen (as the latter increases blossom-end rot).
  • Avoid over-fertilizing during early fruiting when blossom-end rot is more likely to occur.

Share your advice, questions, and comments on blossom-end rot below.

Read more about tomato problems and plant care on our Tomatoes page.

Tomato Blossom-End Rot


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