Blossom-End Rot in Tomatoes

One of the most common tomato problems, blossom-end rot displays a sunken spot on the blossom end (opposite of the stem end) that turns flattened, black, and leathery.

It is a serious disorder that can affect up to 50% of the fruit in some cases. The cause is a lack of calcium absorption due to various factors related to soil nutrients and fluctuations in soil moisture.

How to Identify Blossom-End Rot

Blossom-end rot
University of Florida
Institute of Food and Agricultural Sciences
Blossom-end rot
University of Florida
Institute of Food and Agricultural Sciences
  • Dry, darkened, leathery patch on tomato fruit opposite the stem end.
  • During ripening stages first appears as a small water-soaked spot on the blossom end.
  • As the spot grows, it turns darker and becomes sunken and leathery.
  • The leathery spot can become flattened.

Causes

  • Is caused by a lack of sufficient uptake of calcium.
  • The lack of calcium for the rapidly maturing fruit causes tissues to break down.
  • Moisture fluctuations such as those caused by irregular irrigation can contribute to the problem.
  • Too much nitrogen can cause over-rapid plant growth contributing to the problem.
  • Soils with high amounts of soluble salts can decrease calcium uptake.

Preventative Measures

  • Avoid large fluctuations in soil moisture by consistent watering (around 1-inch per week is a good starting point).
  • Keep soil pH around 6.5.
  • Add calcium to soil by spreading crushed eggshells around the plant, by applying bone meal, or use agricultural or dolomitic lime, which is readily available where lawn fertilizers are sold.
  • To preserve soil moisture spread a protective layer of a material on top of the soil. Organic mulches such as leaves, grass clippings, straw, bark, and similar materials are excellent and improve the soil.
  • Avoid damaging root systems by not cultivating too close to the plant

Treatments

Natural remedies

  • Keep consistent soil moisture
  • Mulching around plants.

Chemical treatments

  • Application of calcium to foliage hasn't proven to be effective.
  • Avoid over-fertilization during early fruiting, especially with ammoniacal forms of nitrogen because excess ammonium ions reduce calcium uptake.
  • Since the problem is physiological in nature, fungicides and pesticides are useless as treatment.

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Credits for technical content

  1. The Ohio State University Extension
  2. Cornell University's Vegetable MD Online



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