Tomatoes Black on Bottom (Know Causes & Fixes)

Watching the healthy reddish tomatoes suddenly have a black end on the bottom can take the hell out of you.

But do you know that most growers face tomatoes with blossom end rot once in a while 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.

Two to three tomato with black bottom is hanging in a vine
Blossom end rot in tomatoes is not due to disease or pests but a physiological disorder.

I found my belly hit with pain when I saw all tomatoes with the blossom end rot on the farm. And I had to dump all the rotten tomato fruits in the yard. 

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

After identifying it, I could not turn a blind eye and tried every means to save other seasonal fruit.

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?

Whether in soil acidity maintenance, watering pattern, or nutrient supply, everything has to be as tomatoes demand.

Tomatoes require a sufficient supply of calcium for healthy fruits. The plants cannot avoid the black bottom if they develop calcium deficiency.

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

While referring to water, you need not let the tomatoes go through underwater or overwater conditions.

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.

Irregularity in the watering schedule leads the plant to suffer from stress.

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

And while trying to correct the dry spell, you may make the roots of tomatoes overwatered.

When an inconsistent watering schedule persists, tomatoes undergo stress which directly affects the tomatoes and leads to the end rot of the fruit.

2. Transpiration Problem 

Increased or decreased leaf transpiration can also destroy the entire harvest of tomatoes. 

Transpiration occurs on the foliage above the ground and is responsible for transferring 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.

3. Fertilization Problem

Tomatoes are a vigorous feeder of nutrients, but an unbalanced ratio of fertilizer supply or dose causes the black bottom to appear in the fruit.

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

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

Fertilizers play a significant role in determining the availability of calcium, as salts from fertilizers can obstruct the absorption rate of roots.

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.

4. Temperature Stress

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

When the heat increases beyond 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.

You might wonder why every cause ends in nutrient uptake. It is because calcium deficiency is the leading cause of rot.

5. Soil Composition Problem

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.

Also, the number of elements like aluminum and manganese up-levels toxicity. 

The soil in the container gets dry much faster than the ground, so they have a higher probability of getting dehydrated and compact.

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

With that said, the compactness of the soil also has adverse effects on the root system of the tomatoes.

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.

6. Low or High Humidity

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

A high transpiration rate leads the entire plant to shift the focus on the leaves, and water carrying the nutrients reaches the leaves instead of the fruit.

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.

So it is better to keep the humidity to a level that is neither too high nor low.

7. High Light Intensity

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

For the production of healthy fruits, light plays an important role, 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.

Excess light damages the fruit’s cells, creating a suitable environment for the growth of the external pathogen.

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.

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. 

The main culprit for the blossom end rot is calcium which can be covered by supplying from external sources.

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.
  • Watering the soil regularly for at least two weeks also 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.
A container consisting of soil with shreds of egg shells over the soil with a pot containing plant above the container.
Eggshells can be an excellent option to increase the calcium content of the soil, but it takes time to decompose.
  • You can also amend the soil with a mixture of coffee grounds and eggshells.

According to a horticulture educator at the University of Illinois, blossom end rot is common in large and long varieties like Roma.

How to Prevent the Black bottom on Tomatoes?

The black bottom of tomatoes does not connect with disease and bacteria.

And you can even eat the tomatoes with blossom end rot by scrapping off the damaged part in the earliest stage. 

But why take the risk? Try to stop black rot in tomatoes from the get-go by maintaining the optimum environment as below. 

  • Provide your tomato plant with direct sunlight for at least 6-8 hours, and try to avoid high intensity.
  • Maintain the humidity not too high and too low, within the range of 65-85%.
  • Try to keep the temperature within the range of 18.3-32.2ºC in its entire growing season, while 21-25ºC temperature ensures high-quality fruit.
  • You can water the tomatoes consistently to prevent the plants from being deprived of water.
  • Allow an inch of water per week during the growing stage and slow it down to twice a week during fruit-bearing.
  • Tomatoes demand nitrogen at vegetative growth but require less during fruit set.
  • 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.
  • The soil for tomatoes should be light, loamy, well-draining, and slightly acidic to neutral with a pH of 6.0-7.0.
Ensure that the plant can transport the nutrients to the fruits without intervention to prevent end rot.
  • Apply the mulch of straw, woodchips, or sawdust to ensure the moisture remains in the soil to the optimum level. 
  • Thin the indeterminate variety of tomatoes after they have set flowers and follow second and third pruning every 10-14 days.
  • Tomatoes are open to the attack of pests like mites, thrips, aphids, and beetle, which is controllable by spraying neem oil and insecticidal soap.
  • Different fungal and bacterial diseases like blight and wilt affect the tomatoes, which can be treated by discarding the affected part and spraying copper-rich fungicide. 


As a garden crop, Tomatoes are readily available 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.

So it is better to maintain suitable conditions and grow tomatoes like Celebrity, Jet Star, and other cherry varieties.

Keep your tomatoes always plump and reddish.

If you have tomato plants with yellow leaves, you need to know how to fix it!

Happy Gardening!

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