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Tomato Rot (How to Cure & Prevent) – GIY Plants

Tomato rot on bottom of tomatoes on plant

Tomato rot, also known as blossom-end rot, is a distressing condition for tomato growers, as it can potentially ruin the first tomatoes of the season.

Although it commonly affects tomatoes, blossom-end rot can also occur in other crops such as peppers, watermelon, and eggplant.

Tomato fruit with blossom-end rot will develop a soft, brown, water-soaked spot at the bottom (blossom end) of the fruit. It’s impossible to miss, as left untreated, blossom end rot on tomatoes will become more sunken, black, and leathery.

Although it looks scary, tomato rot isn’t caused by a disease and can be prevented and stopped.

What Causes Tomato Rot?

Recent research shows that environmental stresses such as salinity, drought, high light intensity, heat, excessive ammonia, etc. are the main causes of blossom-end rot – and not calcium deficiency, as is widely believed. [1]

According to the research, excessive environmental stresses create a high amount of reactive oxygen species (e.g. hydrogen peroxide), which leads to high oxidative stress in plants and eventual cell death.

As cells die, the plasma membranes break, causing calcium to leak. Calcium deficiency, thus, is a symptom and byproduct of cellular death, not a cause of it.

This is important as many people believe that blossom-end rot is caused solely by calcium deficiencies, and can be cured by simply adding powdered milk, crushed egg shells, lime, bone meal, or other forms of calcium to the soil.

Adding calcium alone does not prevent blossom-end rot, and it can actually do more harm than good, as excess calcium inhibits magnesium and potassium absorption.

Excess calcium also increases soil acidity, which may result in stunted growth.

Adequate calcium, of course, is still essential for plant growth and development. Calcium imbalances can further degrade a plant’s ability to transport nutrients and maintain cellular structures, which further leads to fruit tissue death.

How to Treat Tomato Blossom-End Rot

Rotten tomatoes are not reversible and there is no cure, so it’s best to immediately remove affected fruits so that the plant may concentrate energies on producing new healthy fruit.

Blossom-end rot also occurs inside the fruit, leading to black pulp without any obvious external symptoms. Regardless of where you find tomato rot, take immediate preventative action.

When it comes to tomato rot, the old adage, “an ounce of prevention is worth a pound of cure” holds true.

How to Prevent Tomato Bottom Rot

How to prevent tomato rot on bottom of tomatoes

Tomato rot on the bottom of fruits can be prevented with the following practices, which mainly focus on reducing environmental stressors (rather than purely on calcium intake):

  • Avoid adding more salts to the soil. A common gardening myth is that a little Epsom salt will help prevent tomato rot. This is untrue, as Epsom salt can increase salinities in the soil, which actually prevents calcium and water uptake, increasing the chance for blossom-end rot.
  • Avoid droughts by watering evenly and consistently. Keep soils consistently moist, but not soggy. Droughts lead to higher oxidative stresses in plants, which kills plant cells.
  • Avoid extreme sunlight and heat. As temperatures rise in the summer, blossom-end rot occurs more frequently. High temperatures and UV radiation increase rates of photosynthesis and transpiration in leaves, causing water to be directed toward leaves rather than fruits. These factors cause oxidative stress, which contributes to blossom-end rot.

70-75°F (21-24°C) are ideal daytime temperatures for tomatoes. If temperatures consistently rise above 92°F (33°C), consider partial shading or growing tomatoes in containers indoors.

Heat-tolerant tomato varieties such as Summer Set, Heatmaster, and Phoenix also do better in high heat.

  • Avoid over cultivation and overwatering, which may physically damage the roots (e.g. root rot in the case of overwatering). Damaged roots have a hard time taking up nutrients and water, which contributes to oxidative stress and blossom-end rot.
  • Maintain slightly acidic soil pH between 6.0-6.5. Tomatoes with pH outside this range produce higher levels of reactive oxygen species (ROS), which lead to oxidative stress. Soil pH also affects nutrient absorption, making it harder for plants to produce essential antioxidants found in tomatoes such as ascorbate. [2]
  • Avoid overfertilization, as most soils already contain sufficient calcium in the soil. Remember that calcium leakage is a symptom and not a cause of blossom-end rot.

Over-fertilization, especially with nitrogen-heavy fertilizers, creates excessive foliage growth, increasing transpiration, and directing nutrients and moisture towards leaves rather than fruit. Lack of water and nutrients cause oxidative stress in fruits.

If you must fertilize, avoid ammonium-based fertilizers and use a low-nitrogen ratio fertilizer (e.g. NPK 5-20-5 or 4-12-4).

Home Remedy for Tomato Blossom End Rot

Common home remedies for tomato blossom-end rot include Bonide Rot Stop (a commercial product), powdered milk, crushed egg shells, lime, bone meal, Epsom salt (which actually does not contain calcium), or other forms of calcium.

Before using these products, it’s important that you actually test to see if your soil actually lacks calcium.

Most soils actually have sufficient calcium available, and it’s the plant’s inability to absorb the calcium available which is the problem.

While there is no magic bullet for solving blossom-end rot, focusing on calcium alone is generally not sufficient.

More important may be focusing on the environmental stressors that lead to blossom-end rot.


[1] Saure, M. C. (2014). Why calcium deficiency is not the cause of blossom-end rot in tomato and pepper fruit – a reappraisal. Scientia Horticulturae, 174, 151–154. https://doi.org/10.1016/j.scienta.2014.05.020.

[2] Zhang, Y. K., Zhu, D. F., Zhang, Y. P., Chen, H. Z., Xiang, J., & Lin, X. Q. (2015). Low pH-Induced Changes of Antioxidant Enzyme and ATPase Activities in the Roots of Rice (Oryza sativa L.) Seedlings. PLOS ONE, 10(2), e0116971. https://doi.org/10.1371/journal.pone.0116971.

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