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Tomatoes Black on Bottom (Know Causes & Fixes)

Do you know that most growers occasionally face tomatoes with blossom end rot in their gardening journey?

In general, tomatoes have a black bottom due to calcium deficiency triggered by inconsistent watering, excess transpiration, low or high pH level, and high nitrogen in the soil. To fix it, maintain routine watering habits and treat the soil with calcium-rich fertilizer.

My tomatoes displayed black to brown tissues on the bottom of shrunken, wrinkled, and thickened fruits.

So stay with me till the end of this piece before your harvest goes in vain!

Why Does a Tomato Turn Black on the Bottom?

The plants cannot avoid the black bottom if they develop calcium deficiency.

Blossom end rot in Tomatoes
Blossom end rot occurs due to high soil moisture, pest attacks, or faulty soil.

However, calcium deficiency does not come alone, as different factors trigger the lack.

Here are some factors significantly responsible for inviting blossom end rot in tomatoes.

1. Inconsistent Watering

As the roots of tomatoes may rot in overwater conditions, it can affect the total nutrient uptake of the plant.

Unlike overwatering, roots underwater conditions have no medium to transport nutrients to the fruit through the stem, leading to drier and more compact soil.

In the absence of a medium, your tomatoes have already entered the phase of calcium deficiency.

Practical Solution

  • Tomatoes need watering 1-2 inches a week.
  • Do not mist leaves in winter; prolonged wet leaves invite microbial invasion.
  • Always inspect the plant before watering to prevent overwatering.

2. Transpiration Problem 

Transpiration occurs on the foliage above the ground and transfers water along the nutrients to the fruits and leaves.

When the transpiration increases from the foliage, the entire nutrients and water flow toward the leaves.

The defense action makes the leaves receive all the nutrients, depriving the fruits of the nutrients.

But low transpiration also affects the nutrient uptake, and lead results in the entire wilting of the plant.

Here, the green part transpires more than usual, captivating the entire calcium along the water and depriving the calcium in the fruit.

Practical Solutions

  • Increase humidity with a humidifier or place the pot over a water-filled pebble tray to cool down the plants’ surroundings.
  • Avoid exposure of plants to high temperatures or direct sunlight.
  • Cover the plants with cloths during windy days, as wind promotes the transpiration rate.

3. Fertilization Problem

Nitrogen for tomatoes should be around 120 lb/acre. And a slight change in the quantity leads to overgrown foliage.

So better apply 10-10-10 N-P-K fertilizer during the growth and 5-10-10 N-P-K during the flowering and fruiting.
But we cannot blame nitrogen alone for the calcium deficiency because a higher concentration of potassium and ammonium also affects fruit’s calcium uptake.

Besides, the salts also accumulate near the root and obstruct calcium from entering the root fibers.

Practical Solutions

  • Flush the excessive salt accumulated in the soil with distilled water 4-5 times a week during the growing season.
  • Wet the soil a day before fertilizing for better absorption of nutrients.
  • Follow the use recommendations for fertilizers.

4. Temperature Stress

Tomatoes are tropical crops that love warmer temperatures, more than 65ºF, but not exceeding the maximum range.

When the heat exceeds the requirement, tomato plants grow the transpiration rate as a defense mechanism.

By doing so, the plant shifts its entire focus to the leaves, decreasing the reach of calcium to the fruit.

However, the cold temperature does more damage than the extreme one because it inhibits the total nutrient uptake from the soil.

Practical Solutions

  • During hot summer days, mist the plant frequently or place a humidifier near them.
  • Use frost blankets to prevent cold stress.
  • Mulching can be beneficial to keep the soil moist during hot days.

5. Soil Composition 

Tomatoes prefer loamy soil rich in compost and acidic to neutral soil.

But the nutrient supply decreases when the soil becomes highly acidic after repeated plantation in the same ground.

tomato seedling
Besides acidity, the alkaline soil marks the deficiency of potassium and micronutrients like boron, copper, zinc, and iron.  

Also, several elements like aluminum and manganese have up-level toxicity. 

Additionally, in compact soil, the roots do not get an area to expand their fibers, and the passage for the water flow ceases making the entire plant nutrient deficient.

Practical Solutions

  • Add 4-8 inches of organic manure, compost, or worm casting into the soil before planting.
  • Tilling the soil upside down before planting is a good practice for making the soil loose and microbe-free.
  • Space the tomatoes 3-5 feet apart for better absorption of water & nutrients.

6. Low or High Humidity

Tomatoes thrive well in low humidity, but humidity below 65% puts pressure on the leaves to transpire more.

Moreover, high humidity decreases the rate of transpiration and suffocates the plant.

And decreased transpiration means that your fruit and the entire plant will die due to a lack of water and nutrients.

Practical Solutions

  • Mist the plant frequently during summer, but avoid evening misting to prevent rots.
  • Use a humidifier to increase humidity levels, but do not forget to assess the humidity level with a hygrometer.
  • Maintain the humidity not too high and too low, within the 65-85% range.

7. High Light Intensity

Light does not directly affect the tomatoes. It indirectly creates a suitable environment for the blossom end rot to land.

Light plays an important role in producing healthy fruits, but an intensity of more than 650 footcandles damages the fruit cell.

In the presence of damaged cells, fruits can not function normally, which causes calcium deficiency in the end.

Damaged fruit cells can also be a home for external pathogens and pests to rest on, hampering the entire fruit.

Pests and disease are not the root cause of blossom end rot but can be the secondary cause as the pathogens enter the fruit from the spots.

Practical Solutions

  • Avoid overexposure of direct sunlight to plants, as it can sunburn the foliage.
  • Cover the plants with transparent plastics during midday on hot summer days.
  • Direct sunlight of 6-8 hours is favorable for tomato plants.

How Do You Fix the Black Bottom on Tomatoes?

You must know that bottom-end rot occurs mainly at the beginning of the seasonal growth and affects the fruits attached to the vines. 

Moreover, tomato fruits with blossom end rot are safe to eat by removing the infected part, as it is not a pathogenic infection.

So, try the following tips to fix end rot before the tomato ripens and affects other fruits.

  • Remove all the tomatoes affected by the end rot to shift the focus of the plant towards healthy fruits.
  • Water tomatoes deeply so that the water reaches the roots and maintains constant moisture in the soil to allow the recovery of plants.
A container consisting of soil with shreds of egg shells over the soil with a pot containing plant above the container.
Eggshells can be a good option to increase the calcium content of the soil, but it takes time to decompose.
  • Watering the soil regularly for at least two weeks can reverse the situation.
  • Alternatively, apply calcium nitrate to the tomatoes as a top dressing to boost the calcium level.
  • You can also mix powdered milk into the watering can as an instant solution to calcium deficiency.
  • As for the pH level, apply garden lime if the soil is highly acidic and organic compost for alkaline soil to return to its original self.

From Editorial Team


Tomatoes are readily available as a garden crop and have a high fruit-producing ability.

But these plants can disappoint you with black rot on the blossom end induced by a calcium deficiency in the fruits.

However, calcium deficiency is not only the culprit alone, as different factors trigger the rot by enabling the situation to make the plants unable to uptake the calcium.

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